A six-inch banana layer cake frosted with dark chocolate ganache and drizzled with homemade caramel sauce. Topped with flaky sea salt, dark chocolate buttercream, and banana chips.
Preheat the oven to 350 degrees and line the bottoms of three six-inch cake pans with parchment paper. Then, butter and flour the bottom and sides of each pan.
Whisk together the dry ingredients (flour, baking powder, baking soda, and salt) in a medium size bowl and set aside.
Using an electric mixer, cream together the butter and both sugars for 3-4 minutes until it's light and fluffy. With the mixer on low speed, add eggs, then egg white, one at a time and mixing to combine after each addition. Add the vanilla extract and the Greek yogurt and mix.
Alternate adding half of the flour mixture, the buttermilk, then the other half of the flour mixture, beating to incorporate after each addition. Fold in the mashed bananas.
Divide the batter evenly among the three cake pans and tap pans on the counter to remove air bubbles. Bake at 350 degrees for 35-40 minutes, until a toothpick inserted into the center comes out with just a few moist crumbs attached. Let cakes cool in pan for 5-10 minutes, then turn out onto a wire rack to cool completely.
Place chocolate chips in a medium size glass bowl.
Heat heavy cream and butter in a small saucepan over medium heat, stirring frequently. When butter is completely melted and the mixture is heated through (bubbles will start to form at the sides of the pan, but don't let it develop into a full boil), remove from heat and pour over the chocolate chips. Let stand for 5 minutes, then whisk until smooth.
Using an electric mixer, beat the ganache on medium-high speed for a couple more minutes. Chill until ganache reaches a spreadable, frosting-like consistency. This won't take too long - stir it every 5 minutes or so to prevent it from hardening completely.
Over medium heat, melt the sugar in a medium saucepan. Stir frequently with a wooden spoon until melted (it will begin to clump together then melt completely into an amber-colored liquid).
Reduce heat to low and add butter (the sugar may bubble and splatter when the butter is added, this is okay). Continuing stirring until the butter is melted and incorporated completely with the melted sugar.
While continuing to stir the mixture, slowly pour in the heavy cream (the mixture will bubble and splatter again). Mix until incorporated, then increase heat to medium again. Allow caramel to boil for another minute or so, stirring occasionally.
Remove the caramel from the heat and stir in the vanilla extract and salt. Pour into a heatproof jar or bowl and let cool.
Using an electric mixer, beat the butter until light and fluffy. Add powdered sugar and cocoa powder gradually, mixing on low until incorporated. Add melted chocolate and vanilla, then beat to combine. Finally, add heavy cream one tablespoon at a time. Increase speed to high and beat the frosting until smooth.
Using a sharp serrated knife or a cake leveler, remove the rounded tops of each cake. Place the first layer on a cake board, using a small amount of ganache or frosting to attach.
Spread an even layer of ganache on top of the first layer, then top with a second layer of cake and another layer of ganache. Finally, stack the top layer of the cake, cut side down.
Spread a thin layer of ganache (crumb coat) on the top and sides of the cake to lock in any crumbs and to even/smooth out the sides of the cake. Chill for 20 minutes.
Using an offset spatula, finish frosting the top and sides of the cake with the remaining ganache. To get a smooth finish, dip your spatula in a glass of very hot water and quickly wipe it with a paper towel before running it around the edges of the cake. Chill the cake again for about 20 minutes.
Use the dark chocolate buttercream (or ganache) to attach banana chips all around the bottom of the cake.
Check the consistency of the caramel and warm it up in the microwave for a few seconds at a time, if necessary. You want the caramel to drip fluidly, but slowly off a spoon. Spoon the caramel around the edges of the cake, pushing it to the edge so that it drips down the sides of the cake. Then, fill in the middle of the top of the cake with caramel. Sprinkle with flaky sea salt.
Using a pastry bag fitted with a large, open star tip, pipe the dark chocolate buttercream in swirls around the edge of the cake. Top with banana chips as desired.
* 1/4 cup of milk with 1 teaspoon of lemon juice or white vinegar can be substituted for buttermilk. Mix them together and let stand for 5 minutes before using.