Ingredients :
Banana Layer Cake Recipe (adapted from Sally’s Baking Addiction)
1 1/2 cups ripe bananas, mashed – about 3 large bananas (450g)
2 teaspoons of lemon juice (8g)
3 cups all-purpose flour (375g)
1 teaspoon of baking powder (4g)
1 teaspoon of baking soda (6g)
1/2 teaspoon of fine salt (3g)
1 cup unsalted butter, room temperature (226g)
1 cup of granulated sugar (200g)
2/3 cup light brown sugar, packed (133g)
3 large eggs, room temperature (168g)
2 teaspoons of vanilla extract (8g)
1 and 1/2 cups sour cream, room temperature (380g)
3/4 cup mini chocolate chips – mixed with 1 teaspoon flour (130g)
Chocolate Buttercream Frosting:
1 cup semi-sweet chocolate chips, melted and cooled (180g)
2 cups or 4 sticks unsalted butter, room temperature (452g)
1 cup unsweetened cooking cocoa (100g)
1 teaspoon of vanilla extract (4g)
1/2 teaspoon of fine salt (3g)
5 cups powdered sugar (625g)
1/2 cup heavy cream (120g)
Chocolate ganache:
1/4 cup semi-sweet chocolate chips (45g)
1/4 cup heavy cream (60g)
Additional filling/decorations
1/3 cup mini chocolate chips
2 fresh bananas, sliced

Instructions :
Banana Cake Layers:
First prepare the banana cake layers. Preheat oven to 350°F/175°C and grease and line 3 8-inch cake pans. Put aside.
Mash 3 large bananas with a fork or blender and mix with 2 teaspoons of lemon juice. This prevents the bananas from browning. Put aside.
In a large bowl, whisk together 3 cups flour, 1 teaspoon baking powder, 1 teaspoon baking soda, and 1/2 teaspoon salt. Put aside.
Use a hand mixer or stand mixer fitted with a whisk attachment to beat together 1 cup butter, 1 cup granulated sugar, and 2/3 cup brown sugar. Mix on high speed for about 3 minutes. The mixture should become clearer as air is drawn into it. Use a spatula to scrape down the sides and bottom of the bowl as needed.

Mix 3 large eggs and 2 teaspoons of vanilla extract on medium speed.
Mix in half of the dry ingredients on low speed until just combined.
Add 1 1/2 cups sour cream and mix until incorporated, then mix in the remaining dry ingredients on low speed. Be careful not to overmix the dough once you add the flour. The dough will be rather thick.
Beat in the mashed bananas on medium speed until just combined.
Gently fold in the flour-dusted mini chocolate chips with a rubber spatula until they are evenly distributed throughout the batter.
Divide the batter evenly between the prepared pans. Bake for 26 to 29 minutes or until a toothpick inserted in the center comes out with a few moist crumbs. Remove the cakes from the oven and place them on a rack. Let the layers cool in the pans for 10 minutes, then invert them onto a rack to finish cooling.
If desired, twist each cake layer by cutting it in half horizontally with a serrated knife to make 6 thinner layers.

Chocolate Buttercream Frosting:
Melt the chocolate first so it has time to cool before adding it to the icing. Heat it in 15 second intervals, stirring between each interval until the chocolate is completely melted. Put aside.
Beat 2 cups butter on medium speed for 30 seconds with a paddle attachment until smooth.
Add 1 cup of cocoa, a teaspoon of vanilla extract and 1/2 teaspoon of salt. Mix on low until the ingredients are completely incorporated.
Gradually beat in 5 cups powdered sugar and 1/2 cup heavy cream on low speed. Scrape the sides and bottom of the bowl with a rubber spatula as needed.
Stir in cooled and melted semi-sweet chocolate at low speed until ingredients are completely incorporated and desired consistency is reached. Cover with plastic wrap to prevent crusting and set aside.

Chocolate ganache:
Place 1/4 cup semi-sweet chocolate chips in a heatproof bowl and set aside.
Heat 1/4 cup heavy cream in a heatproof bowl in the microwave for 45 seconds to 1 minute, until steaming and just beginning to bubble. If you don’t have a microwave or prefer to use the stovetop, you can heat the cream over medium heat in a saucepan until it begins to simmer. Remove from fire.
Carefully pour the heavy cream over the chocolate, making sure it is completely covered with cream. Let the mixture sit for 1 to 2 minutes.
Stir slowly until the cream and chocolate are completely combined and the mixture is smooth.
Let cool for about 10 minutes. The mixture should thicken and be slightly warm to the touch.
Assembling this chocolate chip and banana layer cake
Stack and frost the cake layers on a greaseproof cake board, using a dollop of chocolate buttercream to help adhere the first cake layer to the board.
Spread an even layer of chocolate buttercream on each cake layer by stacking them with a large offset spatula and sprinkle 2 tablespoons of mini chocolate chips over the frosting.
Cover the cake with a thin layer of chocolate buttercream. Smooth with a scraper, then chill the cake in the refrigerator (30 minutes) or freezer (5 minutes) until the buttercream is firm to the touch.
Add a second, thicker layer of chocolate buttercream to the cake and smooth it out using a scraper. Chill the cake again in the refrigerator (30 minutes) or freezer (5 minutes) until the buttercream is firm to the touch.
Drag diagonal lines of the cooled, thickened chocolate ganache around the base of the cake with a large offset spatula. Top the cake with banana slices, an extra chocolate ganache swirl, and the remaining mini chocolate chips.