Incredibly Creamy Cake (Karpatka)

Ingredients

• ½ cup water (120 g)
• ½ stick unsalted butter (55 g)
• ½ cup all-purpose flour (60 g)
• 3 large eggs
• 2 tsp sugar (10 g)
• a pinch salt
• 2 egg yolks
• ⅓ cup sugar (70 g)
• 3 tbsp cornstarch (30 g)
• 1⅔ cups milk (400 ml)
• a pinch salt
• a few drops vanilla extract (optional)
• 1 stick unsalted butter, soft (115 g)
• 1½ tbsp sugar (20 g)

Method

1. Combine water, butter, and salt in a saucepan and bring to a boil.
2. Remove from heat, add all flour at once, and stir quickly.
3. Return to medium heat and cook, stirring constantly for 3-4 minutes to dry the dough.
4. Cool dough 5-10 minutes, then beat in eggs one at a time until smooth and glossy.
5. Divide dough into two portions, spread on parchment-lined pans, and bake at 375°F (190°C) for 25-30 minutes until golden. Cool on a rack.
6. Whisk egg yolks with half the sugar and cornstarch until smooth.
7. Heat milk with remaining sugar, salt, and vanilla to just below boiling.
8. Slowly pour hot milk into yolk mixture while whisking constantly.
9. Return mixture to saucepan and cook over medium heat, whisking actively until thickened.
10. Cover pastry cream with plastic wrap pressed on surface and chill completely.
11. Whip soft butter with sugar until pale and fluffy.
12. Add chilled pastry cream gradually, one spoonful at a time, whipping until silky and smooth.
13. Place one choux pastry layer on serving board.
14. Spread mousseline cream evenly on top.
15. Cover with second choux layer and press gently.
16. Wrap and refrigerate overnight to stabilize cream.
17. Dust with powdered sugar before serving.