Karpatka (Polish Custard Cake)

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Recipe courtesy of Anediblemosaic.com
Creme' Mousseline:
  • 5 large egg yolks
  • 2/3 cup granulated white sugar - divided into 1/3 cup + 1/3 cup
  • 7 T. potato starch (I used cornstarch)
  • 2 1/2 cups whole milk
  • 1/4 tsp. salt
  • 2 tsp. pure vanilla extract and vanilla bean paste. If you don't have paste, just increase the vanilla extract.
  • 14 T. butter + 1 tsp. of butter
  • 2 T. granulated white sugar
Choux Pastry:
  • 3/4 C. water
  • 6 T. butter
  • 1/8 tsp. salt
  • 3/4 C. flour
  • 3 large eggs
  • 1 large egg yolk
  • butter to grease pans
  • Powdered sugar for dusting the top of the cake
Start the Crème Mousseline
  1. Add the egg yolks and 1/3 cup sugar to a medium bowl. Use a handheld electric mixer to beat together until the mixture is thick and pale yellow. Beat in the corn starch until well combined.
  2. Add the milk, 1/3 cup sugar and salt to a medium saucepan over medium heat. Bring to a gentle simmer.
  3. Remove the milk mixture from the heat. Gradually, starting with just a couple drops at first, whisk 1 cup of hot milk into the egg yolk mixture. Pour the egg yolk mixture into the pot and whisk in the vanilla extract (and vanilla bean paste if using)
  4. Return the saucepan to the heat, and turn the heat down to low. Whisking constantly, cook until the custard is thickened. This should take less that a minute.
  5. Once thickened, transfer the custard to a bowl and place a piece of plastic wrap directly on top. Cool to room temperature.
For the Choux Pastry
  1. Preheat the oven to  380F. Line the bottom of 2 (8 or 9 inch) springform pans with parchment paper that's trimmed to fit inside. Grease the sides with butter.
  2. Add the water, butter, and salt to a medium, saucepan over medium heat. Once the butter is melted, remove the pan from the heat and stir in the flour all at once. Turn the heat down to low and return the pan to the heat. Cook until the dough forms a ball and leaves a residue on the bottom, about 2 minutes, stirring constantly.
  3. Transfer the dough to a large bowl and let it cool until it's still quite warm, but not too hot to touch, about 5 to 10 minutes. Use a handheld electric mixer to beater in the eggs and egg yolk 1 at a time until fulling incorporated. The resulting batter will be smooth and glossy.
  4. Divide the dough between the 2 prepared pans. Spread the dough out to cover the bottom of each pan, and then use the back of a spoon to spread it unevenly to create divots and peaks (this is so the finished cake looks like the Carpathian Mountains.
  5. Bake until the choux cake is puffed and evenly golden, about 25-28 minutes.
  6. Cool for 10 minutes in the pans, then remove the cakes from the pans and cool completely on a wire rack.
Finish the Creme' Mousseline 
  1. Once the custard is cool, use a handheld electric mixer to cream together the butter and 2 T. sugar in a large bowl until pale and fluffy.
  2. Add a spoonful of vanilla custard at a time and beat until incorporated, continuing until all the custard is mixed. Continue beating until the mixture is light and fluffy, about 5 minutes.
  3. Place a piece of plastic wrap directly on top of the creme' mousseline if the cakes aren't completely cool yet.
Once the choux cakes are completely cool, put 1 of the choux cakes back into a springform pan. Spread the vanilla custard evenly on top. Place the other choux cake on top.
Refrigerate 1 hour before serving, and then remove it from the springform pan. Right before serving, dust the top with powdered sugar.

  • Vanilla Bean Paste Substitute: If you don't have this on hand, simply use more vanilla
  • Potato Starch Substitute: You can use 3 1/2T. of cornstarch instead
  • Choux Pastry Tip: Don't be tempted to swap out the water for milk in the choux pastry for this recipe. Water helps result in a crisper, lighter choux pastry and also prevents over-browning. On the other hand milk in choux pastry acts as a tenderizer, and yields a softer pastry.
  • Creme Mousseline Tip: When you make the creme mousseline, make sure the butter and the pastry cream are the same temperature. Both should be at room temperature, about 70 to 74F.
  • If you don't have two springform pans: If you only have 1 springform pan, you can bake the choux cakes 1 at a time. Just be sure to place a piece of plastic wrap directly on top of the dough while the first cake bakes. Alternatively, if you don't have any springform pans, you can line 2 large baking trays with parchment paper and draw 1 (9-inch) circle on each. Spread the batter out onto the circles you drew and bake that way.