1. Make the pudding: Prepare an ice-water bath; set aside. Whisk together cornstarch, 2 tablespoons granulated sugar, and salt in a small bowl. Whisk eggs in another bowl until smooth; whisk into cornstarch mixture. Set aside.

2. Whisk together milk and remaining 6 tablespoons sugar in a medium saucepan. Bring to a boil over medium-high heat. Slowly pour milk mixture into egg mixture, whisking constantly.

3. Pour mixture back into saucepan. Cook, whisking constantly, over medium-high heat until thickened, about 2 minutes. Remove from heat, and pour through a sieve into a medium bowl. Whisk in butter and vanilla. Set bowl in ice-water bath, and let cool, stirring occasionally, 30 minutes. Pudding can be refrigerated in an airtight container up to 3 days.

4. Make the whipped cream: Put cream into the bowl of an electric mixer fitted with the whisk attachment; beat on medium speed until soft peaks form. Add confectioners' sugar. Beat until stiff peaks form.

5. Assemble the cake: Using a serrated knife, trim tops of cakes level, then cut each in half horizontally, making 4 layers. Place 1 cake layer into the bottom of a straight-sided 4-quart bowl (about 8 inches in diameter and 6 inches high). Spread with 1/2 cup pudding, then with 3/4 cup whipped cream. Arrange 4 banana quarters on top; top with another cake layer. Repeat 3 times, decorating final banana layer with a dollop of whipped cream. Drizzle with chocolate; top with a cherry. Sprinkle with sprinkles and nuts, if desired. Using a large spoon, divide portions among serving bowls. Serve immediately.