Pastry Cream (Day ahead)

1. Heat the milk: In a saucepan, heat milk with half the sugar until just steaming (not boiling)

2. Whisk the egg mixture: In a bowl, whisk together egg yolks, remaining sugar, and cornstarch until smooth.

3. Temper the eggs: Slowly pour a small amount of the warm milk into the egg mixture while whisking. Gradually add the remaining milk, whisking continously.

4. Cook until thickened: Return the mixture to the saucepan and cook over medium heat, whisking constantly, until thick and pudding-like. It should hold lines when whisked.

5. Finish cooking:  Continue cooking for 1-2 minutes more, until smooth and glossy.

6. Finish cream: Remove from heat and stir in butter and vanilla until fully incorporated.

7. Chill: Transfer to a clean bowl, cover with plastic wrap directly on the surface, and refrigerate overnight.

Choux Pastry

1. Preheat the oven: Preheat oven to 400 degree °F (200°C). Line two 9-inch round pans with parchment paper.

2. Heat the base: In a saucepan, combine butter, water, milk, sugar and salt. Bring to a full boil over medium heat..

3. Add the flour: Add flour all at once and stir vigourousely until a smooth dough form and pulls away from the sides.

4. Cook the dough: Continue cooling for 2-3 minutes, stirring constantly, to dry the dough slightly.  A think film will form on the bottom of the pan - this is normal and indicated it's ready.

5. Cool slightly: Transfer the dough to a bowl and let cool for about 5 minutes.

6. Add the eggs: Add beathen eggs a little at a time, mixing well after each addition until fully incorporated. The dough should become smooth, glossy, and fall from the spatula in a soft "V" shape. (You may not need all the eggs)

7. Divide and shape: Divide the dough between the prepared pans (slightly more for the top layer if desired). Spread each portion into a layer using an offset spatula.

8. Create texture: Do not smooth completely- intentionallay create an uneven, rugged surface. This will form the signature Karpatka "mountains" as it bakes.

9. Bake: Bake :400°F (200°C), for 15 minutes. (Refrain from opening the oven during the first 20 minutes due to risk of collapse) then reduce to 350°F (175°C) and bake another 20–25 minutes or until deep golden brown. 

10. Dry the shells: Turn off the oven, crack the door slighlty, and let the layers sit inside for 10-15 minutes fo dry out further.

11. Cool completely. Remove from oven and allow to cool completly before assembling.

Make the Mascarpone Cream

1. Loosen the pastry cream. Remove the chilled pastry cream from the refrigerator and whisk until completely smooth and creamy.

2. Prepare the mascarpone: In a separate bowl, gently stir the mascarpoine just until smooth. (Avoid overmixing as mascarpone can become grainy)

3.  Combine pastry cream and mascarpone: Add the pastry cream to the mascarpone in 2-3 additions, gently folding until fully incorporated and silky.

4. Whip cream: In a clean bowl, whip the heavy cream to soft medium peaks. The cream should hold shape but still be soft and airy.

5. Fold everything together: Gently  fold the whipped cream into the mascarpone mixture in 2-3 additions. 

6. Final texture: Thick, airy, and stable enough to hold peaks and create dimples when shaped.

Assemble the Karpatka

1. Place the bottom choux layer on your serving plate.

2. Add the mascarpone cream. Spoon over the base and spread into a thick layer (about 1 1/2-2 inches)

3. Create the "mountain" texture. Use an offset spatula to lift and shape the cream into soft peaks and valleys-keep it natural, not perfectly smooth.

4. Add cherry jam. Press whole cherries into some of the valleys and spoon a little jam into the crevices. You want small pockets throughout, not a full layer. You can also use a chopstick and swirl the jam into more of a marble.

5. Top with the second choux layer. Place gently over the cream without pressing down.

6. Finish. Dust with powdered sugar just before serving.