In a saucepan, combine water, milk, unsalted butter, sugar, salt, and vanilla extract, then heat over medium heat until it starts simmering. Remove from the heat and add the sifted flour. Mix until no dry flour is left, bring back to the heat, and set it to low.

Cook the dough, mixing with a rubber spatula continuously for 2 minutes or until the dough forms a ball and the bottom of the saucepan is covered with white residue. Remove from the heat.

Place the dough into a large mixing bowl or the bowl of a stand mixer fitted with a paddle attachment. Let it cool down for 10 minutes or until it’s no longer hot to touch but still very warm.

Split the dough into two even parts and spread unevenly between two prepared spring forms. This unevenness will create random bubbles on the surface of the cake layers during the baking, which represent the Carpathian mountains. If you’re using one spring form, cover the second part of the dough with a plastic wrap while the first part is baking.

Bake for 25-27 minutes or until reaching a deep, even golden-brown color on top. Remove from the oven and leave to cool down for 10 minutes before removing it from the form onto a cooling rack to cool down completely. Repeat the process if using only one spring form.

Place milk, half of the sugar, and salt into a saucepan and heat over medium heat until simmering.

Meanwhile, combine the second half of the sugar with the cornstarch in a heatproof mixing bowl, then add the egg yolks and vanilla. Whisk until a homogenous consistency is reached without cornstarch lumps.

When the milk start simmering, remove from the heat and slowly add approximately ½ of it to the egg yolk mixture while whisking vigorously to temper the eggs. Then, pour the egg mixture back into a saucepan with the hot milk.

Cook over low heat for 5-9 minutes, whisking consistently until the mixture become pudding-like in consistency, then cook for about 2 minutes. Don’t stop whisking. If lumps appear, whisk vigorously and they will dissolve.

Remove from the heat and pour the mixture into a large, shallow dish. Cover the pastry cream with plastic wrap so they touch each other and let it cool down to room temperature. You can place it into the fridge to speed up the process. However, if you cool it down too much, you need to bring it back to room temperature before the next step.

In a stand mixer fitted with a whisk attachment (or use a hand mixer and a large mixing bowl), beat the butter at room temperature with 15g of sugar until white and fluffy.

Whisk the pastry cream (IMPORTANT! The pastry cream should be at room temperature at this point or it won’t mix well with the butter) until it becomes smooth again.

Then, add the pastry cream a couple of tablespoons at a time to the butter and whisk every time on medium until incorporated. Continue until all pastry cream is combined with the butter. Scrape the sides and the bottom of the bowl, then beat again for 10 seconds.

Onto a serving plate, place the clean ring from the spring form that you used to bake the cake layers. Cover the sides inside the ring with parchment paper, if desired, as it will make it easier to release the cake after chilling.

Place the first layer (the one that is less puffed up) inside. Press slightly to make it flatter.

Place all cream on top and even it out.

Cover with the top layer and press a little bit to attach it. Then, refrigerate for 2-3 hours or until the cream has set. Remove from the ring, peal the parchment paper if used, dust with powdered sugar, and serve.