Ingredients

5 large egg yolks

2/3 cup granulated white sugar (divided into 1/3 cup + 1/3 cup)

7 tablespoons potato starch

2 1/2 cups whole milk

1/4 teaspoon salt

2 teaspoons pure vanilla extract

2 teaspoons vanilla bean paste (or more vanilla extract)

200 grams unsalted butter (at room temperature; about 14 tablespoons + 1 teaspoon)

2 tablespoons granulated white sugar

3/4 cup water

6 tablespoons unsalted butter

1/8 teaspoon salt

3/4 cup all-purpose flour

3 large eggs

1 large egg yolk

Butter (to grease the pans)

Powdered sugar (for dusting on top)

Instructions

Step 1: Start the crème mousseline by beating together 5 egg yolks and 1/3 cup sugar in a medium bowl until thick and pale yellow. Then, beat in the potato starch until combined.

Step 2: In a saucepan, heat the milk, remaining 1/3 cup sugar, and salt over medium heat until it reaches a gentle simmer. Remove from heat.

Step 3: Gradually whisk about 1 cup of the hot milk into the egg yolk mixture, starting with a few drops at a time. Then pour this mixture back into the saucepan. Whisk in the vanilla extract and vanilla bean paste.

Step 4: Return the saucepan to low heat and cook, whisking constantly, until the custard thickens, about a minute. Transfer the custard to a bowl, cover with plastic wrap directly on the surface, and cool to room temperature.

Step 5: Prepare the choux pastry by preheating the oven to 380°F. Line and grease two 8 or 9-inch springform pans with parchment paper and butter.

Step 6: In a saucepan, combine water, 6 tablespoons butter, and 1/8 teaspoon salt over medium heat. Once the butter melts, remove from heat and stir in the flour all at once. Return to low heat and cook, stirring constantly, until the dough forms a ball and leaves a residue on the bottom (about 2 minutes).

Step 7: Transfer the dough to a bowl and let cool for 5 to 10 minutes until warm but not hot. Using a handheld mixer, beat in eggs and egg yolk one at a time until fully incorporated and the batter is smooth and glossy.

Step 8: Divide the dough evenly between the prepared pans. Spread it out to cover the bottoms, then use the back of a spoon to create uneven peaks and divots for the characteristic “mountain” look.

Step 9: Bake for 25 to 28 minutes until puffed and golden. Cool in pans for 10 minutes, then remove from pans and cool completely on a wire rack.

Step 10: Finish the crème mousseline by beating the room-temperature butter with 2 tablespoons sugar until pale and fluffy. Gradually add the cooled custard in spoonfuls, beating until fully combined and the mixture is light and fluffy (about 5 minutes).

Step 11: If the choux cakes are not completely cool, cover the crème mousseline with plastic wrap. Once cakes are cool, assemble by placing one cake into a springform pan and spreading the custard evenly on top. Place the second cake on top.

Step 12: Refrigerate the assembled cake for 1 hour before serving. Remove from the pan and dust with powdered sugar just before serving.

Tips & Variations

For deeper vanilla flavor, use vanilla bean paste instead of extract or a combination of both for the custard.

Create the characteristic peaks on the choux pastry by spreading the dough unevenly before baking—it adds a rustic mountain appearance.

If potato starch is unavailable, cornstarch is a suitable substitute for thickening the custard.

To add a fresh touch, serve with berries or a drizzle of chocolate sauce.

FAQs

Can I make the custard ahead of time?

Yes, the custard can be prepared a day in advance and refrigerated. Just be sure to cover it with plastic wrap directly on the surface to prevent a skin from forming.