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a mocha hazelnut layer cake with a slice being taken out of it on a cake lifter spatula

mocha hazelnut Milk Bar-style layer cake

Rebecca
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.
Day 1: Make the hazelnut praline paste and the cake. Wrap and refrigerate the cake.
Day 2: Make the hazelnut chocolate frosting, hazelnut crunch, chocolate ganache, and the coffee soak. Assemble the cake.
The cake needs to freeze for at least 3-5 hours after assembly and defrost for 2-3 hours before slicing. Take it out 2-3 hours before serving to thaw.
Note: Estimated times do not include time to chill or defrost the cake.
5 from 2 votes
Prep Time 2 hrs
Cook Time 30 mins
Assembly time 30 mins
Total Time 3 hrs
Course Dessert
Cuisine American
Servings 1 6" cake

Ingredients
  

hazelnut praline paste

  • 115 grams hazelnuts (1 cup, skins removed)
  • 115 grams sugar (½ cup)
  • 30 grams water (⅛ cup)
  • 2 TBSP vegetable oil

basic Milk Bar chocolate cake

  • 113 grams unsalted butter (8 TBSP, room temp)
  • 225 grams sugar (1 cup + 2 TBSP)
  • 60 grams brown sugar (¼ cup, tightly packed)
  • 3 large eggs (at room temp)
  • 121 grams buttermilk (½ cup, at room temp, see notes for substitution)
  • 105 grams neutral oil (½ cup + 3 TBSP)
  • 5 grams vanilla extract (1¼ tsp)
  • 154 grams cake flour (1¼ cups)
  • 70 grams cocoa powder (½ cup)
  • 6 grams baking powder (1½ tsp)
  • 7 grams diamond crystal kosher salt (1¾ tsp)

chocolate hazelnut frosting

  • 80 grams semi-sweet baking chocolate (3 oz)
  • 220 grams unsalted butter (1 cup, room temp)
  • 320 grams powdered sugar (3 cups)
  • 60 grams cocoa powder (½ cup)
  • 1 tsp kosher salt
  • 60 grams whole milk (4 TBSP)
  • 200 grams hazelnut praline paste (½ cup + 2 TSBP)

hazelnut crunch (optional)

  • 125 grams hazelnuts (1 cup, skins removed)
  • 40 grams neutral oil (3 TBSP + 2 tsp)
  • 20 grams brown sugar (1 TBSP + 1 tsp, tightly packed)
  • 60 grams frosted flakes cereal (¾ cup)(a cheaper alternative to feuilletine)

chocolate stout ganache (optional)

  • 250 grams 72% dark chocolate (9 ounces)
  • 45 grams heavy cream (3 TBSP)
  • 70 grams freshly brewed coffee (⅓ cup)

coffee soak

  • ½ cup freshly brewed coffee
  • ¼ cup sugar

Instructions

Hazelnut Praline Paste

  • Heat oven to 350°F. Toast hazelnuts on an un-greased sheet pan for 15 minutes, shaking the pan every 5 mins to prevent burning.
  • Transfer the toasted hazelnuts to a sheet pan lined with a silicone mat, grouping them closely together in the center.
  • Combine sugar and water in a skillet and use a spatula to mix them together so the sugar is fully hydrated. Place the skillet over medium-high heat. Do not stir. The sugar will begin to bubble, and after a few minutes will take on an amber color. Gently swirl the pan so the sugar doesn’t burn until it's entirely caramel in color.
    If you start to see wisps of smoke that’s a good sign that you should be done.
  • Quickly and carefully pour the liquid sugar mixture over the hazelnuts on the silicone mat. If the mixture doesn’t coat all the hazelnuts, pick up the loose ones and place them on top of the liquid or pick up the edges of the silicone mat to herd them into the middle. The caramel will harden quickly, so work fast.
  • Once the praline has cooled, peel it off the mat (it should come up easily!) and break it into pieces. Place the pieces in the bowl of a food processor and puree until a peanut butter-like texture forms. Drizzle in oil with the food processor running, and puree until smooth.
  • Transfer to an airtight container and leave at room temp until ready to use. (Praline paste can be stored in an airtight container at room temp for several months.)

Chocolate Cake

  • Preheat your oven to 350°F. Generously spray a 13x9" rectangular cake pan and line it with parchment paper or a silicone mat. Try to keep the edges and corners as wrinkle free as possible.
  • Place the butter, brown sugar, and granulated sugar in the bowl of your stand mixer. Use the paddle attachment to cream the butter and sugars together on medium-high speed for 2-3 minutes (set a timer!) until light in color. Scrape down the sides of the bowl about halfway through and again at the end.
  • Add the eggs one at a time, beating on medium-high for at least 1 full minute after each egg is added. Scrape down the bowl before and after adding each egg.
    After all three eggs are in, beat the mixture on high for 4 minutes.
    Seriously, set a timer here. Let the mixer do its thing. Scrape down the sides and bottom of the bowl when the 4 minutes are up.
  • While the mixer is running, whisk together buttermilk, neutral oil, and vanilla extract.
  • With the mixer at medium speed, slowly pour the liquid mixture into the mixer bowl. It should take you about 2-3 minutes to pour it all in.
    Scrape down the sides of the bowl, then increase the mixer speed to medium-high and beat for 2-3 minutes until the mixture has almost doubled in size.
  • In a separate bowl, mix the cake flour, cocoa powder, baking powder, and salt. With the mixer running on a very low speed, use a measuring cup (½ cup or ¾ cup recommended) to slowly add the dry mixture to the mixing bowl.
    Once all of the dry mixture has been added and the batter comes together — don’t over mix! — scrape down the sides of the bowl making sure to get the bottom too, then mix on low speed for 45-60 seconds just to make sure there are no lumps.
  • Pour the cake batter into the prepared sheet pan and use a spatula to spread it in an even layer, making sure to get it into the corners.
  • Bake at 350°F for 30-35 minutes. Halfway through the bake time, rotate the pan.
    At 30 minutes, jiggle the pan slightly — the center of the cake should not be jiggly. If the center of the cake still looks jiggly, leave it in an additional 5 minutes. (To test for doneness with a thermometer, you're looking for 200-210°F in the center).
  • Let the cake cool completely in the pan on a wire rack. When cool, remove from the pan and wrap in plastic wrap (including the parchment paper). The cooled cake can be stored in the fridge for up to 5 days.

Chocolate hazelnut frosting

  • Melt the chocolate over a double boiler, or in the microwave (10-second bursts until melted).
    Set aside and let cool to room temp.
  • Use the stand mixer with the paddle attachment to combine softened butter, powdered sugar, cocoa powder, and salt until a dark, firm mass of chocolate has formed.
    Then, set a timer for 2-3 minutes and cream at medium-high speed until smooth and fluffy. Scrape down the sides of the bowl.
  • Reduce mixer speed as low as it can go and slowly stream in the milk. Increase the speed to medium-high and beat for additional 5 minutes (again — set a timer!).
    The mixture should be silky smooth and glossy. As always, scrape down the sides and bottom of the bowl. Scrape down the mixer paddle too.
  • Add the hazelnut praline paste and cooled melted chocolate to the mixing bowl and stir on low speed until the frosting is fully combined and no streaks of chocolate or hazelnut remain.
  • If not using immediately, store in an airtight container the fridge. To use: Let come to room temperature and re-whip using the mixer with paddle attachment at medium speed for 3-4 minutes.

Hazelnut crunch

  • Toast the hazelnuts on an un-greased sheet pan at 350°F for 10-15 minutes.
  • Puree the toasted hazelnuts in a small food processor with the oil, brown sugar, frosted flakes, and salt until a wet, sandy texture is achieved.

Chocolate Stout Ganache (Day 3)

  • Finely chop the chocolate and place it in a heat-proof bowl.
  • Combine the freshly brewed coffee and heavy cream in a small pot over medium heat. Bring to a low simmer.
  • Pour the hot coffee mixture over the chocolate, and stir in circles until completely smooth and no lumps remain.
  • Use the ganache immediately. If you aren’t ready to use it right away, you can reheat it in the microwave in 15-second bursts, stirring in between.

Coffee soak

  • Prepare a cup of coffee using whatever method you prefer. I use a French press, but you do you.
  • Pour coffee into a small bowl, add sugar and stir until dissolved.

Cake assembly

  • Use a 6″ cake cutter to cut two 6″ rounds out of the refrigerated chocolate cake. Place the ring in the center of a cardboard cake round, and line the inside of the ring with a cake collar (a 20″ strip should be enough).
  • Use the remaining cake scraps to create the bottom layer of cake. Break them up, and crumble them with your hands, pressing them tightly, especially into the bottom corners, to create an even, solid foundation for your cake.
  • Use a spoon or pastry brush to apply ⅓ of the coffee soak to the cake layer.
    Then apply ½ of the chocolate stout ganache, and use a small offset spatula to spread it all the way to the edges of the acetate.
    Top the ganache with ½ of the hazelnut crunch, again taking care to make sure it’s pressed up against the acetate.
    Finally, pipe ⅓ of the chocolate hazelnut frosting in a spiral over the crunch layer.
  • Carefully place the second cake layer on next. If one of the two cake rounds is messier or more uneven than the other, use that one.
  • Take the second 20″ acetate cake collar and insert it into the first one. Tuck it just under the top edge of the second cake layer so it stays in place.
  • Now repeat the layers: ⅓ of the coffee soak, the rest of the chocolate stout ganache, the rest of the hazelnut crunch, and pipe in another spiral of the chocolate hazelnut frosting.
  • Insert the final cake round. Place whichever side is flatter and smoother facing up. Then apply the rest of the coffee soak, and pipe a final spiral layer of chocolate hazelnut frosting. Use a mini offset spatula to smooth or create designs in the top layer of frosting.
  • Take the whole cake and put it in the freezer for at least 3-5 hours, or overnight. If you plan on keeping it in the freezer for longer than overnight, cover the top with saran wrap.
  • Before serving, remove cake from freezer and defrost for at least 3 hours.
    When ready to serve, slide the cake ring up to remove it and peel off the acetate sheets.

Video

Notes

  • If you don't have buttermilk, mix ½ cup whole milk with ½ TBSP lemon juice or vinegar about 5 mins before you need to use it in the recipe.
  • I find it's easiest to remove the cake ring after the cake has been in the freezer for about 2 hours. The outside of the cake will have frozen enough that the acetate won't come off (or you can tape the acetate closed with masking tape) but the cake also hasn't expanded so much that the ring is stuck in place. 
  • The original version of this recipe used a chocolate stout ganache instead of a coffee ganache. To make a chocolate stout ganache, simple replace the coffee in the ganache with chocolate stout. 
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