Banana Pudding Bundt Cake

Preheat oven to 325°F (170°C).

In the bowl of a stand mixer fitted with the paddle attachment, beat butter and sugars at medium speed until light and fluffy, 3 to 4 minutes, stopping to scrape bottom and sides of bowl. Add eggs, one at a time, beating well after each addition. Beat in vanilla bean paste.

In a large bowl, whisk together flour, ground wafers, salt, and baking powder. With mixer on low speed, add flour mixture to butter mixture in three additions alternately with buttermilk, beginning and ending with flour mixture, beating until just combined after each addition.

Spray a 10-cup Bundt pan with baking spray with flour. Spoon batter into prepared pan, smoothing with an offset spatula. Firmly tap pan on a kitchen towel-lined counter several times to settle batter.

Bake until a wooden pick inserted near center comes out clean, 1 hour and 10 minutes to 1 hour and 25 minutes, covering with foil halfway through baking to prevent excess browning. Let cool in pan for 10 minutes. Invert cake onto a wire rack, and let cool completely.

Using a serrated knife, cut cooled cake in half horizontally. Using a cake lifter or cake board, remove top half of cake, and reserve. Using a small spoon, scoop out center from bottom half of cake, creating a 1½-inch-wide, 1-inch-deep trench. (Reserve cake crumbs for garnish, if desired; see Note.)

Spoon Banana Crème Mousseline into a pastry bag fitted with a large star piping tip (Ateco #826). Pipe into cake trench and on bottom half of cake as desired. Top with banana slices. Place top half of cake onto filling and banana.

Spoon Vanilla Whipped Cream into a pastry bag fitted with a large star piping tip (Ateco #826). Pipe onto top half of cake as desired. Garnish with cake crumbs, banana slices, and vanilla wafers, if desired. Cover and refrigerate for up to 3 days.

In a medium bowl, combine bananas and milk; cover and refrigerate for at least 8 hours or up to overnight.

Strain milk into a medium saucepan, discarding solids. Heat milk over medium heat until steaming. (Do not boil.)

In another medium bowl, whisk together sugar, cornstarch, and salt; whisk in egg yolks until smooth. Gradually whisk in half of hot milk. Whisk egg mixture into remaining hot milk in pan. Bring to a boil over medium heat, whisking frequently. Cook, whisking constantly, until thickened and an instant-read thermometer registers 185°F (85°C), about 3 minutes. Remove from heat.

Whisk in 2 tablespoons (28 grams) butter in two additions until melted and smooth; whisk in vanilla bean paste.

Strain mixture through a fine-mesh sieve into a large bowl, discarding solids. Cover with plastic wrap, pressing wrap directly onto surface of pastry cream to prevent a skin from forming. Refrigerate until thick and cold, at least 4 hours, or overnight.

Let pastry cream and remaining ½ cup (113 grams) butter stand at room temperature for 20 to 30 minutes. (Butter should be slightly soft and the same temperature as pastry cream.)

In the bowl of a stand mixer fitted with the paddle attachment, beat softened butter at medium speed until smooth, about 1 minute. Gradually add pastry cream, beating until combined after each addition and stopping to scrape bottom and sides of bowl. Refrigerate until thick but pipable, about 1 hour, stirring every 30 minutes. Use immediately.