• Preheat oven to 425°F.
• Mix together salt, garam masala, cumin, coriander, turmeric, and cayenne in a small bowl and set aside.
• Place peeled, diced potatoes in a pot of generously salted cold water. The potatoes should be completely submerged with at least 1" of water above them. Bring the pot to a boil, then reduce to a simmer and cook for 12-15 minutes until the potatoes are fork-tender.

  When the potatoes are done, drain them and set them aside in a large mixing bowl.
Pro-Tip: If you start cooking the onions when the water for the potatoes starts to boil, the timing will align perfectly for the potatoes to be ready to drain at the same time as you finish cooking the onion mixture.
• Heat a large, high-sided skillet over medium-low heat. Let the skillet heat up for a couple minutes, then melt the butter. Add the diced onion and cook, stirring occasionally, for about 8-10 minutes. Turn the heat down if the onions start to take on darker color. A little color is fine, but the darker they get the sweeter they become.
• When the onions are translucent, stir in the spice mixture and add the minced garlic, ginger, and Serrano pepper to the pan.

  Cook, stirring frequently for 3-5 minutes until very aromatic.
• Add the onion mixture to the bowl with the potatoes. Add the cilantro, peas, and lemon juice and stir until the mixture is evenly combined. Some of the potatoes will break apart, but that's a good thing. Taste the mixture and add more salt or pepper if needed.
There's no need to defrost the frozen peas before adding them to the filling. The heat from the potatoes and onion mixture will defrost them as you mix. Plus, the whole thing is about to go in the oven anyway. The peas will have plenty of opportunities to defrost!
For best results, refrigerate the filling so that it's cold when you assemble the pie. If you assemble it with warm filling, the heat from the filling will begin warming up the fat in the pie crust and puff pastry which will make it soggy instead of flaky.

Assembly

It is very important that pie crust and puff pastry are as cold as possible before baking. Work quickly and get the pie in the oven ASAP.
If the oven isn't at the right temperature yet when the pie is assembled, stick the whole pie in the fridge or freezer until you're ready to bake it.
• Take your defrosted puff pastry out of the fridge about 15-20 minutes before you plan to use it so you can unfold it without cracking.
• Divide the potato mixture evenly between the two pie shells, filling them right up to the top. Flatten the mixture in each pie shell so there's not a big heap in the center.
• On a lightly floured surface carefully unfold the first puff pastry sheet. It should still be lightly chilled, but not frozen. Use a rolling pin to stretch the sheet out an additional inch, trying to pinch the creases back together as best you can.
• Brush the egg wash around the border of the bottom pie shells. Take one of the sheets of puff pastry and drape it over one of the filled bottom pie shells. Use scissors or a knife to trim off any excess pastry, using the edge of the pie tin as a guide. Press the tines of a fork around the edge to seal the puff pastry and pie shell together. Brush the top all over with egg wash, then use a small knife in an up-and-down motion to cut 3-5 long slits in the top of the pie to let steam escape.
Try not to get any egg wash inside the vent holes or on the outer edge of the pie crust. Egg wash acts like glue and if you get it on the outer rim where the two crusts are joined together, you'll glue all the flaky layers together.
• Place the pies on a cookie sheet and bake in a 425°F degree preheated oven for 40-45 minutes. When the puff pastry has puffed up and achieved a dark golden brown color, your pie is done. If the top of the pie seems like it's browning too much, drape a sheet of aluminum foil over it in the oven.
• Remove pies from the oven and let cool for 15-20 minutes before slicing and serving. Serve with lime yogurt sauce on the side.