In a medium saucepan, whisk together egg yolks and granulated sugar until thick and pale, about 3-4 minutes. Gradually stir in hot milk while mixing. Return the mixture to medium heat, stirring constantly until it thickens, around 5-7 minutes. Once thickened, remove from heat, add vanilla extract and butter, stirring until smooth. Let the custard cool completely, about 30 minutes.

In a medium saucepan, combine water, unsalted butter, and salt over medium heat, bringing it to a gentle simmer. Once melted, remove from heat and quickly stir in sifted all-purpose flour. Mix vigorously until the dough forms a ball and pulls away from the sides, about 2-3 minutes. Let it cool slightly for 10 minutes before gradually adding eggs one by one, mixing until fully incorporated.

Preheat your oven to 380°F (190°C) and line two baking sheets with parchment paper. Divide the choux pastry dough equally between the sheets, spreading it out to form rectangles. Use a spoon to create peaks and valleys on the surface for a rustic look. Bake for 25-28 minutes or until the pastry is puffed and golden brown, then allow it to cool completely on a wire rack.

Once the choux layers are fully cooled, carefully place one layer on a serving platter. Spread an even layer of the cooled custard over the first layer to create a luscious filling. Place the second choux layer gently on top, aligning it with the edges of the first layer.

Dust the top of your assembled Karpatka Carpathian Cream Cake generously with powdered sugar for an elegant finish. Refrigerate for at least 1 hour before serving. Slice into portions and enjoy!