Preheat oven to 350°F (175°C) and line two 9-inch cake pans with parchment paper, greasing the sides.

In a medium bowl, whisk together all-purpose flour, baking soda, and salt.

In a large bowl, beat 1/2 cup softened butter and granulated sugar on medium speed for 3 minutes until pale and fluffy.

Add eggs one at a time, beating well after each addition, then stir in 1 teaspoon vanilla extract.

Mash bananas in a small bowl and alternately add bananas and sour cream to the butter mixture, beginning and ending with bananas, mixing on low until just combined.

Add flour mixture in three additions, mixing on low speed until just combined after each addition.

Divide batter evenly between pans, smooth tops, and bake for 32–37 minutes until a toothpick comes out with minimal crumbs.

Cool cakes in pans for 10 minutes, then invert onto wire racks to cool completely.

Make frosting by beating 1/2 cup softened butter with peanut butter, then gradually add powdered sugar, heavy cream, 1 teaspoon vanilla, and salt; beat until fluffy.

Place one cake layer on a plate and spread 3/4 cup frosting on top, then stack second layer and frost top and sides with remaining frosting.

Combine chocolate chips, 1/2 cup butter, and corn syrup in a small saucepan over low heat; stir until smooth then cool slightly.

Pour chocolate over the frosted cake, letting it drip down the sides; smooth any pooled chocolate with an offset spatula.

Refrigerate cake for at least 30 minutes to set, then let stand 15 minutes at room temperature before slicing.