Crème Brûlée Cake
At first glance this cake appears deceptively plain, but it is lush and rich. Delicate layers of vanilla bean cake are layered with German buttercream, a naughty combination of vanilla custard whipped together with a lavish amount of butter. Permeated with the flavors of vanilla, burnt sugar, and cream, one bite will lure you into its downy embrace.
Make the caramelized sugar shards that decorate the top of this cake the day you want to serve it. If the weather is rainy or excessively humid, make the sugar shards as close to serving as possible. They will keep 3 to 4 hours on a dry day, and 1 to 2 hours if it is humid, before they start to get sticky.
SERVES 8 TO 10
3 cups [360 g] cake flour
3 tsp baking powder
1 tsp fine sea salt
3/4 cup [180 ml] whole milk, at room temperature
3/4 cup [180 g] sour cream, at room temperature
1 cup [220 g] unsalted butter, at room temperature
1/4 cup [60 ml] canola or vegetable oil
2 1/4 cups [450 g] sugar
2 Tbsp vanilla bean paste
6 egg whites, at room temperature
BURNT SUGAR SYRUP
1 cup [200 g] sugar
1 cup [240 ml] warm water
MASCARPONE GERMAN BUTTERCREAM
3 cups [720 ml] whole milk
6 Tbsp [60 g] cornstarch
3 eggs and 3 Yolk
3 cups [600 g] sugar
1/4 tsp fine sea salt
3 cups [660 g] unsalted butter, at room temperature
1/2 cup [120 g] mascarpone cheese, at room temperature
2 Tbsp vanilla bean paste
CARAMELIZED SUGAR SHARDS
1 cup [200 g] sugar.
Position a rack in the center of the oven. Preheat the oven to 350°F [180°C]. Coat three 8-in [20-cm] or 9-in [23-cm] round cake pans with nonstick cooking spray. Line the bottoms with parchment paper.
Sift together the cake flour, baking powder, and salt into a medium bowl. In a separate medium bowl, whisk together the milk and sour cream.
In a stand mixer fitted with the paddle attachment, beat the butter and oil together on medium speed until creamy. Increase the speed to medium-high, add the sugar, and beat until light and fluffy, 3 to 5 minutes. Beat in the vanilla paste and vanilla extract. Stop the mixer and scrape down the sides of the bowl. With the mixer on medium-high speed, beat in half of the egg whites, just until combined. Stop the mixer and scrape down the sides of the bowl again. Beat in the remaining egg whites just until smooth.
With the mixer on low, beat the dry ingredients into the batter in three additions, alternating with two additions of the sour cream mixture and beginning and ending with the dry ingredients. Beat for 10 to 15 seconds after each addition, just until the batter is smooth. Do not overbeat, or the final cake will be tough. Divide the batter evenly between the prepared cake pans, using a spatula to smooth the tops. Bake for 25 to 30 minutes for 8-in [20-cm] layers or 22 to 28 minutes for 9-in [23-cm] layers, until a wooden skewer inserted into the center of each cake comes out clean.
To make the Burnt Sugar Syrup:
While the cake layers are baking, combine the sugar and 1/4 cup [60 ml] of the warm water in a 2-qt [2-L] stainless-steel saucepan over medium heat. Cook, gently swirling the pan occasionally, without stirring, until the sugar dissolves and starts to caramelize. Increase the heat to high and boil until it turns a golden amber color, 4 to 6 minutes. Immediately remove the pan from the heat and pour in the remaining 3/4 cup [180 ml] warm water. Stir, using a long-handled wooden spoon to avoid being splashed with hot caramel, until the caramel dissolves.
(The Burnt Sugar Syrup can be used immediately, or, if making it in advance, refrigerate in a covered container for up to 1 month. Just make sure to warm it up before brushing it on your cake layers.)
When the cake layers are done, transfer the pans to wire racks and let cool for 10 minutes. Invert the layers onto the racks, remove the pans, and peel off the parchment paper. While the cake layers are still warm, brush the bottoms and sides of each layer with the warm Burnt Sugar Syrup, making sure to use all the syrup. Let the cake layers cool completely before filling and frosting.
To make the buttercream:
In a medium heatproof bowl, whisk together 1/2 cup [120 ml] of the milk with the cornstarch to dissolve. Whisk in the eggs and egg yolks. Set aside.
In a 3-qt [3-L] stainless-steel saucepan, stir together the remaining 21/2 cups [600 ml] milk and the sugar. Stir over medium heat until the sugar is dissolved. Increase the heat to medium-high and bring to a boil. Remove from the heat and briskly whisk 1/2 cup [120 ml] of the hot milk mixture into the egg mixture to temper it. Whisk in an additional 1/2 cup [120 ml] hot milk. When the mixture is smooth, whisk in the remaining milk and the salt. Return the mixture to the saucepan.
Over medium-high heat, whisk the custard continuously until it thickens and comes to a low boil, with large bubbles that rise to the surface, plopping slowly. Continue whisking, without stopping, for 1 to 2 minutes. This will thicken the custard and cook the eggs completely. Do not cook any longer than 2 minutes, as the cornstarch will actually start to lose its thickening ability and the custard will become thin and soupy as it cools.
Pour the warm custard through a finemesh sieve into a large bowl. Cover with plastic wrap, pressing it onto the surface of the custard to prevent a skin from forming. Refrigerate until very cold, at least 3 hours and preferably overnight.
When cold and firm, scrape the custard into the bowl of a stand mixer fitted with the whisk attachment. Beat the custard on low for a few seconds to loosen it. Increase the mixer speed to medium and beat in the softened butter, 2 Tbsp at a time. Continue beating, adding the butter a little at a time, until it is fully incorporated and the buttercream is fluffy and thick enough to spread. Beat in the softened mascarpone and vanilla bean paste, just until combined.
To finish the cake:
Place the first syrup-soaked cake layer on a cardboard cake round or cake stand, bottom-side up. Top with one-fourth of the buttercream, spreading it over the surface of the cake in an even layer all the way to the edges. Top with the second cake layer and spread with the same amount of buttercream. At top with the third cake layer. Frost the top and sides of the cake with a thin coat of buttercream to form a crumb coat. Refrigerate for 30 minutes to set.
Spread the top and sides of the cake generously with the remaining buttercream, smoothing it evenly with an offset spatula. Refrigerate the cake in a covered cake carrier for up to 24 hours before serving. Let the cake come to room temperature 1 to 2 hours before slicing. Up to 1 hour before serving, decorate the top of the cake with broken, caramelized sugar shards. Store at room temperature for up to 2 days (sugar shards may soften and start to melt after a few hours, but are still tasty).
To make the Caramelized Sugar Shards:
Sprinkle the sugar in an even layer in a large, heavy-bottomed stainless-steel saucepan. Heat over medium-high heat until it begins to melt around the edges. Stir with a fork (the sugar may clump or form lumps, but will smooth out as it melts). When the sugar has melted into a syrup, bring to a boil and cook until it turns a golden amber caramel color (about 340°F [170°C] degrees on an instant-read candy thermometer). Immediately pour the syrup onto a rimmed baking sheet, tipping the pan so the syrup coats about half of the pan in a thin, even layer. Let cool completely, about 15 minutes. (I choose not to grease the pan, as the oil tends to leave a slick film on the sugar shards.)
To dislodge the hardened sugar, tap gently with a small mallet or the back of a heavy knife to break it into large pieces. Once broken, you can dislodge the caramel shards with your fingers or the tip of an offset spatula. To make smaller pieces, place the large shards in a self-sealing plastic bag and give them a few firm whacks with the mallet or knife. Use the shards and any caramel dust to decorate the top of the cake.