Doberge Cake

Preheat oven to 175°C (350°F). Grease and line seven 23cm (9-inch) round cake pans with parchment paper (bake in batches if you do not own seven pans). In a stand mixer, cream 226g softened unsalted butter and 400g granulated sugar on medium speed for 3 minutes until light and fluffy. Add 4 room-temperature whole eggs one at a time, beating 30 seconds after each addition, then mix in 2 teaspoons of vanilla extract. Whisk 315g cake flour, 2 teaspoons baking powder, and 1 teaspoon fine sea salt in a separate bowl; alternate adding the dry mix and 240ml whole milk to the butter mixture on low speed, starting and ending with dry ingredients, until just combined (do not overmix, as this will create tough cake layers). Divide batter evenly (approximately 200g per pan) across prepared pans, spread into thin, uniform layers. Bake 10-12 minutes until edges are pale golden and a toothpick inserted in the center comes out clean. Cool layers in pans for 5 minutes, then transfer to wire racks to cool completely to room temperature (about 30 minutes).

In a heavy-bottomed saucepan, heat 720ml whole milk over medium-low heat until it just starts to steam (do not boil, 4-5 minutes). While milk heats, whisk 6 room-temperature egg yolks, 150g granulated sugar, and 48g cornstarch in a heatproof bowl until smooth and pale yellow. Slowly pour 120ml of the hot milk into the egg mixture while whisking constantly to temper the eggs and prevent curdling, then pour the entire tempered egg mixture back into the saucepan. Cook over medium-low heat, whisking nonstop, for 3-4 minutes until custard thickens to a pudding-like consistency that coats the back of a spoon. Remove from heat, stir in 56g unsalted butter until fully melted, then split the custard evenly between two glass bowls. Stir 113g chopped semi-sweet chocolate into one bowl until fully melted and smooth; stir 1 tablespoon lemon zest and 3 tablespoons fresh lemon juice into the second bowl until combined. Press plastic wrap directly onto the surface of both custards to prevent skin formation, then chill in the refrigerator for 1 hour until fully set.

In a clean stand mixer fitted with a whisk attachment, beat 226g softened unsalted butter on medium speed for 2 minutes until pale and creamy. With the mixer running on low speed, gradually add 360g sifted powdered sugar and 40g sifted unsweetened cocoa powder, mixing until fully incorporated with no dry lumps. Increase speed to medium-high, add 60ml room-temperature heavy cream, 1 teaspoon vanilla extract, and 1/4 teaspoon fine sea salt, then whip for 3-4 minutes until light, fluffy, and easily spreadable; add 1 extra teaspoon of cream if the frosting is too thick to spread smoothly. Set buttercream aside at cool room temperature until ready to assemble the cake.

Place one fully cooled cake layer on a 23cm (9-inch) cake board or flat serving plate. Spread 1/3 of the chilled chocolate custard (approximately 150g) evenly across the top of the layer, leaving a 3mm (1/8-inch) border from the edge to prevent filling from oozing out when stacked. Top with a second cake layer, and spread 1/3 of the chilled lemon custard (approximately 150g) evenly across it, maintaining the same small border. Repeat this alternating pattern—chocolate custard, cake layer, lemon custard, cake layer—until all 7 cake layers and all custard are used, ending with a plain cake layer on the very top (3 chocolate custard layers and 3 lemon custard layers total). Press down gently on the top layer to level the entire stack, then chill in the refrigerator for 20 minutes to let the fillings set slightly before frosting.

Remove the chilled cake stack from the refrigerator. Use a metal offset spatula to spread 1/3 of the chocolate buttercream (approximately 230g) in a thin, even layer across the entire top and sides of the cake. This first coat is designed to trap loose cake crumbs, so it does not need to look perfectly smooth, and some crumb visibility is expected. Return the cake to the refrigerator for 30 minutes until the crumb coat is firm to the touch, which will prevent loose crumbs from mixing into the final smooth frosting layer.

Once the crumb coat is fully set, use the remaining 470g (2/3) of the chocolate buttercream to apply a thick, smooth, even layer across the top and sides of the cake. Hold a metal bench scraper against the side of the cake as you slowly rotate the cake stand to create sharp, clean edges, and smooth the top surface with the offset spatula. For a classic Doberge finish, create soft, subtle swirls on the top of the cake with the tip of the offset spatula, or leave it perfectly smooth. Return the fully frosted cake to the refrigerator to chill for 1 full hour before slicing and serving, to let all layers and fillings set firmly.