Mocha Hazelnut Layer Cake (Milk Bar Style)

Chocolate cake with a coffee soak, layers of hazelnut frosting, crunchy filling, and a coffee ganache make this Mocha Hazelnut layer cake a real showstopper.

I've been itching to make one of Milk Bar's spectacular, bare-sided triple-layer cakes ever since my sister and I dropped $75 at the opening weekend of Milk Bar's L.A. store to try "a bit of everything."

If you haven't seen a Milk Bar cake before, they're towering cakes with bold layers of frosting and crunchy fillings visibly between equally thick, plush layers of cake.

Christina Tosi, the brilliant mind behind Milk Bar's spectacular creations is known for inventive desserts that are rich and decadent without being tooth-achingly sweet. They're great.

The official Milk Bar All About Cake cookbook has been staring me down for months now so, when Jimmy requested a coffee hazelnut birthday cake, I finally had a good reason to crack it open.

I was determined to deliver something unique. The wrinkle: Jimmy loves hazelnut but doesn't like Nutella (weird, I know!) so I had to find a way to incorporate the hazelnut flavor without using a Nutella-based recipe. 

In the end, I used Milk Bar's basic Chocolate Cake recipe, the Stout Ganache from the Pretzel Layer Cake (with coffee instead of stout), the Chocolate Hazelnut Frosting from the Banana-Chocolate-Hazelnut Cupcakes recipe, and I adapted the crunchy filling from the German chocolate cupcakes to use hazelnuts instead of pecans.

The coffee soak, which is used to keep the cake layers moist, I made up on the fly. And thus, a Milk Bar-style mocha hazelnut layer cake was born.

But is a 3 layer mocha hazelnut Milk Bar-style layer cake practical?

Oh, absolutely not! There are five-and-a-half components that need to be created before you can even begin assembling this cake. If you're looking for a practical cake, go for this moist chocolate pound cake, this old fashioned vanilla pound cake, this ginger-pumpkin spiced cake or this rosemary chocolate chip cake or do a basic sheet pan cake with frosting.

To make this just slightly more practical, though, I've noted which two components are optional (the ganache and the hazelnut crunch). Bare minimum, all you need to make are the cake, the frosting, and the coffee soak. But the two optional components are pretty simple so if you have the time/energy/bandwidth, I do recommend making them.

Pros and cons of a Milk Bar cake

What I really loved about the process of building a Milk Bar cake was that the assembly itself was so simple that my brain was free to focus more on creating the individual components without feeling frazzled or rushed.

Yes, there are multiple components but because they can all be prepped ahead, or easily created right before assembly, you don't feel like you're constantly fighting against a clock or trying to time everything perfectly or convince icing to stick on a warm cake.

I also appreciated how efficient Milk Bar recipes are. Where usually you'd bake and trim 3 separate round cakes for a layer cake, the Milk Bar method has you bake one rectangular cake and use a 6" cake-cutting ring to cut your layers out of it.

But, like I said, this is not the kind of cake you can — or should — make all in one day. Here's how I did it:

• Day 1: Make the hazelnut praline paste for the frosting
• Day 2: Make the frosting and the cake, refrigerate both
• Day 3: Make the hazelnut crunch, the coffee ganache, and the coffee soak. Re-whip the frosting. Assemble.

A two-day timeline would look like this:

• Day 1: Make the hazelnut praline paste and chocolate cake. Refrigerate cake.
• Day 2: Make the frosting, hazelnut crunch, coffee ganache, and coffee soak. Assemble.

What I didn't love about some of the recipes in the Milk Bar book is that they call for really specific, often expensive, hard-to-find ingredients like hazelnut praline paste and Feuilletine and don't include recommendations for cheaper alternatives. I've noted below where I've made more affordable alterations to the recipes, but if you'd rather spend the money to just have the right thing without any extra steps, you do you.

Making the chocolate cake

While you can probably use any 13x9" chocolate cake recipe here, the official Milk Bar chocolate cake recipe produces a uniform cake with an exceptionally flat surface. Most cakes end up with a slightly domed top that needs to be sliced off for layering, but the Milk Bar recipe produces a flat-topped cake that requires zero trimming.

Make sure that you really let your mixer run for as long as the recipe says between steps to get a beautifully airy cake batter. If you use a different chocolate cake recipe or end up with a dramatically domed top to your cake, use a serrated knife to trim it flat.

The cool thing about these cakes is that you don't need to make 3 separate cakes to get your layers. You punch the top two layers out of a rectangular cake using a 6" cake cutter, and then use the remaining scraps to form the bottom layer.

If your cake top is only slightly domed, it should be fine. These aren't meant to be perfect-looking cakes, anyway. A little unevenness is okay.

TIP: Double-triple check the size of your sheet pan. In doing some research for this post I ran across several blog posts and forums that say the Milk Bar recipes are sometimes inconsistent with the size of sheet pan they call for (they call for a "quarter sheet pan"). But I found it works perfectly in a 13x9" rectangular cake pan, so I recommend using that.

Money Saving Alteration: The recipe calls for a ½ cup of buttermilk, but since the frosting calls for 4 tablespoon whole milk, you can use ½ cup whole milk mixed with ½ tablespoon lemon juice or vinegar to replicate the chemical reaction of buttermilk without spending money on two kinds of milk. Simply mix the two together about 5 minutes before the recipe calls for it to be used.

The secret to true hazelnut chocolate frosting

This frosting, which I borrowed from All About Cake's Banana-Chocolate-Hazelnut cupcakes is the icing on the cake here, literally and figuratively. It's buttery and light, and the hazelnut praline paste adds a rich, sweet flavor that doesn't make your teeth ache.

The only thing is... hazelnut praline paste is both expensive and hard to find. I couldn't find it in any grocery store near me, and online it was going for almost $20 for 11 ounces, which meant that, even though I was doubling the batch, I'd have leftover praline paste, which I didn't need.

So... I made my own praline paste. Exactly the amount I needed, with none leftover. And honestly, if you have the right tools, I think you should do that too. It's really not that hard.

What is hazelnut praline paste? It's hazelnut praline (toasted hazelnuts coated in a hardened caramel) pulverized in a food processor until the nuts release their oils and it reaches a peanut butter-like consistency.

How to make hazelnut praline paste: First make, make hazelnut praline by toasting the hazelnuts and pouring caramel over them. Once it hardens and cools, break the hazelnut praline into pieces and send them on a trip through the food processor until it turns into a peanut butter-like paste. Store at room temp until you're ready to use it. Boom.

You will need: A food processor (I used my beloved mini-KitchenAid food processor) and a silicone baking mat.

I know it seems complicated and potentially messy, but the caramel is actually really easy to clean up — once it hardens, it comes off the silicone mat without a problem, and if it gets anywhere you don't want it, hot water will melt and dissolve it right off.

Time-Saving Tip: Just buy the pre-made stuff.

How to assemble a Milk Bar-style layer cake

Instead of baking individual cake rounds, Milk Bar cake rounds are cut out of a single 13x9" rectangular cake. The bottom layer of cake is built out of cake scraps inside of the metal cake ring, which you line with the acetate cake collars to hold everything in place.

Start by cutting out your two 6" cake rounds. Then, place the 6" metal cake cutter in the center of a cardboard cake rounds and line it with a sheet of the acetate to hold everything in place.

Order of mocha hazelnut layer cake assembly:

• Layer 1: Cake — Break the remaining cake into chunks, and press it into the bottom of the cake round. Don't be shy here. The cake scraps don't have to be pretty but they do have to support another three layers of cake and frosting. Press 'em in, tear the cake pieces into chunks, crumble them up, and really push them in firmly. Once the cake comes out of the cake ring and you remove the acetate sheets, that bottom layer still has to support the weight of a cake above it. You want a firm foundation!
• Layer 2: Coffee Soak — Use a spoon or a pastry brush to liberally douse the cake layer with ⅓ of your coffee soak. The coffee soak will help the scraps stick together and keep the cake moist.
• Layer 3: Chocolate Ganache (OPTIONAL) — Half of the ganache goes on here. It's a pretty thin layer, spread it as evenly as you can across the surface of the cake.
• Layer 4: Hazelnut Crunch (OPTIONAL) — Half of the hazelnut crunch mixture goes down here — this one's a bit harder to spread so try to get it in an even layer as best you can. I like to make sure I have it around the edges so that there's a visible ring of it on the exterior of the cake.
• Layer 5: Chocolate Hazelnut Frosting — ⅓ of the chocolate hazelnut frosting goes down next. If you made this a day or two in advance it will firm up in the fridge. Loosen it by putting it back in your mixer bowl and beating it at medium speed for 3-4 minutes.

Insert the second cake round (if one of the two cake rounds is messier than the other, use that one).

STOP. DO NOT PASS GO. DO NOT SKIP THIS STEP: Take the second acetate cake collar strip and insert it inside the first one, tucking it behind the second cake round to hold it in place. (I always forget to do this until after I've put the next layer down and it's very annoying to do once the next layer of ganache is down.)

Repeat the order above: Coffee soak, chocolate ganache, hazelnut crunch, and chocolate hazelnut frosting.

The final layer: Place your last cake round on top, with whichever side is smoothest facing up. Apply the rest of the coffee soak, and a final layer of chocolate hazelnut frosting.

And that's it! You're done.

The final step is to stick the whole mocha hazelnut layer cake in the freezer for 3-5 hours

This gives the cake a time to set — the coffee soak freezes, the cake layers get all cozy and meld together.

Before serving, take the cake out of the freezer and let it defrost for 2-3 hours. Before serving, slide the metal cake ring off and peel off the acetate. That's it! You're ready to start slicing!

Use a dish towel dampened with warm water to wipe the knife blade between slices to help make clean cuts, especially if any parts of the center are still a little frozen.

Equipment Notes

• Acetate cake collars — The Milk Bar book calls for 3" tall ones, but I bought 4" ones and found they were just the right height. You'll need two 20" long strips.
• 6" cake-cutting ring — You will use this to cut out your cake layers and also to assemble the base of your cake.
• 8" cardboard cake rounds — You'll need to refrigerate or freeze your cake when you're finished, these are perfect for moving/picking up your finished cake and fitting it in your freezer or fridge.
• Small offset spatula — Since you need to be able to reach down into the acetate tube to spread your frosting and ganache layers, it helps to have a small, easily maneuverable tool on hand.

Practical Tips & Recipe Notes

• Look for hazelnuts that are already peeled. It's much easier to tell when they're toasted, and this way you don't have to try to remove the skins yourself. I use these ones. If you only have hazelnuts with the skins on, wrap them in a towel after toasting and roll them around to remove as much of the skins as you can.
• Pay attention to temperatures: To quickly bring eggs to room temperature, submerge them in warm water for 60 seconds. You'll need the butter to be very soft for both the cake and the hazelnut frosting, so leave it out overnight before use if you can.
• I find it easiest to use a large 18" piping bag to pipe the layers of hazelnut frosting. You're not looking for pretty piping, just an even layer of frosting so no need for piping tips, just cut a wide opening at the bottom. If you don't have a piping bag you can cut a hole in the corner of a large Ziplock bag or use a spatula.
• Neutral oil = canola, vegetable, grapeseed, safflower, or corn. This light extra virgin olive oil also works well. Basically any oil that doesn't have a strong flavor.
• If the second or third cake layers break or crumble when you go to put them inside the acetate, that's okay. Just use cake crumbs to patch any holes. The coffee soak and the ganache and the acetate will hold everything together for you.
• Instead of Feuilletine I used Frosted Flakes cereal. One of those round single-serving cereal cups is exactly the amount you need (60g). My pastry instructor recoiled in horror when I told him I'd made this swap, but given that Christina Tosi is a big proponent of cereal-inspired desserts, I like to think she'd approve!

📖 Recipe

This post was originally published on 11/15/2019.