Preheat the oven to 350 degrees F. Lightly grease
2 (10-inch) cake pans
with 1 teaspoon of the butter. Line the bottoms with parchment paper, and butter the parchment with the other 1 teaspoon butter. Set aside.
Puree the bananas, sour cream
, and vanilla in a food processor
the cake flour, 3/4 cup sugar, baking soda, baking powder, and salt into a bowl.
In the bowl of an electric mixer
fitted with a paddle attachment, cream the remaining 10 tablespoons butter and 1 cup sugar. On medium speed, add the dry ingredients in 3 additions, alternating with the banana mixture, scraping the sides of the bowl and beating well after each addition.
Pour the batter
into the prepared pans. Bake until the cake is lightly browned and bounces back when touched with your fingers, about 30 to 40 minutes, depending upon your oven. Let cool for 10 minutes before turning out onto a wire rack to cool completely. Peel
off the parchment paper.
To assemble the cake, using a long serrated knife, trim off the rounded top of each cake layer to make them flat. Place the bottom layer on a wire rack set over a baking sheet. Spread the Pastry Cream evenly over the top. Place the next cake layer upside down on the first. Wrap the cake around the sides with double layers of plastic wrap to keep the pastry cream from oozing out. Gently press down on the top layer. Remove the plastic wrap
and scrape off any excess pastry cream.
Slowly pour 1 to 1 1/2 cups of the Chocolate Ganache onto the top of the cake, letting it run down the sides. Let sit for 5 minutes, then, in several applications, slowly pour on the remaining ganache until the cake is completely covered. Chill until ready to serve.