Add the water and butter to a small saucepan and bring to a simmer. Add the flour, baking powder, and salt and stir vigorously to bring to a smooth dough. With a spatula, bring the dough to the sides of the pan to release any lumps of flour that may be in there. Then fold it back over and repeat the process until your dough is completely smooth. Once the dough is smooth, continue to cook for a couple of minutes to allow some of the moisture in the dough to evaporate.

You can do this next step by hand, or you can add your hot dough to a standing mixer with a whisk attachment. Pulse the dough several times to release steam. It will help the dough to cool down before adding the eggs. You don’t want the dough to be too hot when adding the eggs because the eggs will curdle.

Once the dough is warm and no longer hot, beat the eggs in one at a time. Make sure the eggs are fully mixed in before adding the next one. You know you have the correct consistency of dough when the dough runs off of your spatula in a v shape.

Now divide the dough evenly between two 9×13 inch (22x33cm) metal baking pans. Do not use glass pans. The choux pastry will not rise properly in the oven if baked in glass. Using a silicone spatula, spread out the dough evenly in the pan. This will take a little bit of patience since the dough is very sticky.

In a 200C/392F preheated oven, bake the pastry for 25 minutes, or until the pastry is golden, puffed up, and dry on the surface. As the name of the pastry indicates, these are supposed to look like a mountain range. Let the pastries cool completely in the pan.

Meanwhile, for the pastry cream, in a small bowl whisk together the egg yolks, 327 ml (1 cup) of milk, flour, and cornstarch. Pass the mixture through a sieve to strain out any lumps.

Combine the remaining milk and granulated sugar in a small saucepan on the stove and bring to a light boil. Then reduce the heat.

Whisking the egg mixture vigorously, whisk in 327 ml (1 cup) of the hot milk to temper the egg yolks. This will keep them from curdling when added to the rest of the milk.

While continuously whisking, pour the tempered egg yolk mixture into the pot. Let it cook over medium heat while continuously whisking. The pastry cream will get thicker and thicker. You’re looking for the consistency of vanilla pudding. You want it to get to the stage where it’s bubbling and burping. Once it reaches that stage, let it cook for a minute or two.

Turn off the heat and stir in the vanilla.

Pour the finished pastry cream into a shallow dish and then cover with plastic wrap. Make sure the plastic wrap directly touches the pastry cream so it doesn’t form a skin. Let the pastry cream come to room temperature. It needs to be at room temperature for the next step to work properly.

Once at room temperature, spoon the pastry cream into a mixer and beat in the room temperature butter a little at a time until it reaches a pale, thick, creamy consistency.

Pour the cream into one of the pastry shells. Spread out the cream evenly.

Before placing the top pastry over the rest of the cake, fill in any gaps with pastry cream on the underside of the pastry where the pastry rose, so there are no gaps when cutting the cake.

Cover and refrigerate for a minimum of 2 hours. Preferably 4-6 for a solid interior. This will make slicing the cake easier.

Before serving, dust with powdered sugar to look like snowcapped mountains. Slice into 12 servings and enjoy. Ciesz się posiłkiem!