Karpatka - Carpathian Mountain Cake

For the pastry cream filling

1. Sift the cornflour (or potato flour) and plain flour into a bowl.
2. In a separate bowl, whisk the egg yolks with the sugar and vanilla, then stir in half of the milk and half of the cream. Pour this mixture into the flour in the bowl and whisk to a custard.
3. In a saucepan, gently heat the other half of the milk and cream, then add the custard mixture, stirring constantly over a low heat for at least 8-10 minutes. It is fine if bubbles form, but make sure it is heating very gently to avoid scrambling. The cream will thicken but keep stirring/whisking. You need to taste it at this stage - if you can still taste flour, keep it on the heat for a little longer and add a little more milk if it becomes too thick. You can increase the heat at this stage but keep whisking. It will continue to thicken once set. Once thick, take the pastry cream off the heat, transfer to a heatproof bowl and allow to cool.
4. Once the custard is at room temperature, tip it into a stand mixer, whisk, and then add the butter, bit by bit, until all the butter is incorporated. Cover the surface with clingfilm so that a skin does not form.
5. Leave to chill overnight in the refrigerator.

For the pastry choux

1. Preheat your oven to 180°C/160°C Fan/Gas Mark4/350°F. Line two 30 x 23cm/12 x 9in baking trays with baking paper.
2. For the choux pastry, combine the water, milk, sugar, vanilla, salt and butter in a small pan and bring to a gentle boil, taking care that the milk doesn’t scald.
3. Once the mixture comes to the boil, add the flour in one go along with the baking powder and be ready to mix this vigorously (I use a wooden spoon). You will end up with a ball of dough that is a little sticky, but keep beating. Beat until it comes away from the sides of the pan, then leave to cool completely.
4. Transfer the ball of dough to a large, clean bowl, or use a stand mixer or food processor. Add the whole eggs to the dough, one by one. Make sure each egg is well mixed into the dough before adding the next one. You should end up with a smooth, thick mixture, somewhere between a batter and a dough.
5. Divide the mixture across the two baking trays. Don’t smooth it out — you are looking for an uneven layer to create the mountains. As it bakes, ridges and furrows will form. Bake for 30–35 minutes until it is golden and well-risen. Switch off the oven and open the door, allowing the steam to escape and the pastry to sit for a few minutes. After this time, take the pastry out of the oven and leave to cool completely.
6. Place one of the choux pastry layers onto a serving platter and spread over a thin layer of marmalade or fruit preserve. Spread over the pastry cream, then place the second layer of choux pastry on the top. Add a sprinkle of toasted almonds and dust with icing sugar, if you like. Cut into rectangles to serve.