Boston Cream Pie

INTRUCTIONS

1. Adjust an oven rack to the middle position and heat the oven to 350 degrees. Grease and flour two 8- or 9-inch round cake pans, line the bottoms with parchment paper, and grease the paper.

2. Whisk the flours, baking powder, and salt together in a medium bowl. Heat the milk and butter together in a small saucepan over low heat until the butter melts. Off the heat, stir in the vanilla and cover to keep warm.

3. In a large bowl, whip the 3 egg whites and the cream of tartar together with an electric mixer on medium-low speed until foamy, about 1 minute. Increase the mixer speed to medium-high and whip the whites to soft, billowy mounds, about 1 minute. Gradually whip in 6 tablespoons of the sugar, about 30 seconds. Continue to whip the whites until they are shiny and form soft peaks, 1 to 3 minutes.

4. In a separate large bowl, whip the 3 egg yolks and the eggs together with an electric mixer on medium-high speed and gradually add the remaining 6 tablespoons sugar, about 1 minute. Continue to whip the mixture until very thick and voluminous, 4 to 6 minutes.

5. Scrape the whipped whole egg mixture on top of the whipped white mixture, then sift the flour mixture over the top. Very gently fold everything together with a large rubber spatula until just combined, about 12 folds. Pour the warm milk mixture against the side of the bowl and continue to fold the batter until evenly combined and no streaks of flour remain, about 8 folds.

6. Immediately scrape the batter into the prepared pans. Bake the cakes until lightly browned and a toothpick inserted in the center comes out with a few crumbs attached, 12 to 18 minutes. (Do not rotate the cakes during baking.)

7. Immediately run a small knife around the edge of the cakes, then flip them out onto a parchment-lined plate (to protect the delicate top). Peel off the parchment paper bottom, flip the cakes right side up onto a wire rack, and discard the parchment. Let the cakes cool completely before filling or frosting, about 2 hours.

8. FOR THE PASTRY CREAM:

Bring the milk to a simmer in a medium saucepan over medium heat. Meanwhile, whisk the egg yolks, sugar, and salt together in a medium bowl, then whisk in the cornstarch until pale yellow and thick, about 30 seconds.

9. Slowly whisk the hot milk into the egg mixture to temper, then return the mixture to the saucepan and cook over medium heat, whisking constantly, until thick and glossy, about 1½ minutes. Off the heat, whisk in the butter and vanilla. Transfer the mixture to a small bowl, press plastic wrap directly on the surface, and refrigerate until chilled and set, about 2 hours.

10. FOR THE GLAZE:

Microwave all of the ingredients together, whisking often, until melted and smooth, 1 to 2 minutes. Let the glaze cool, uncovered, until it is thickened but pourable, about 20 minutes.

11. Line a large baking sheet with parchment paper and top with a wire rack. Place one of the cake layers on the rack. Spread the pastry cream over the cake, right to the edges. Place the other cake layer on top and press lightly to adhere.

Pour the chocolate glaze on top of the cake, letting it drip down the sides. Refrigerate the cake, uncovered, until the chocolate has set, at least 2 hours or up to 24 hours. Before serving, transfer the cake to a cake platter and let sit at room temperature, 30 to 60 minutes.

PREPARING THE CAKE PAN

1. The trick to getting a piece of parchment that fits the bottom of a cake pan is to trace the outline of the bottom of the pan onto the parchment. When cutting out the outline, cut on the inside of the line so that the round fits snugly inside the pan.

2. Grease the inside of the pan evenly with a thin coat of butter or vegetable shortening.

3. Sprinkle flour in the cake pan, then shake and rotate to coat evenly with the flour; shake out any remaining flour.

4. Fit the trimmed piece of parchment into the pan. The butter or shortening, along with the flour, will help the parchment adhere.

MAKING A FOOLPROOF SPONGE CAKE

1. After whipping the egg whites separately from the yolks and whole eggs, gently layer the whole egg mixture on top of the whites in a large bowl, but do not mix together yet.

2. Gently sift the flour mixture over the egg mixtures using a mesh strainer.

3. Use a large spatula to very gently fold the batter together—be careful not to deflate the batter.

4. Pour the warm milk mixture against one side of the bowl and fold until evenly combined and no streaks of flour remain, about 8 more folds.

AFTER THE CAKE IS BAKED AND LAYERED: GLAZING

1. To glaze a cake with chocolate, simply pour the chocolate glaze on top of the cake and let it flow down the sides. Be sure to set the cake on a wire rack over a parchment-lined baking sheet to catch the excess glaze.