How to Make It
Preheat oven to 350 degrees. Grease 2 8” round cake pans. Cream butter and sugar in a stand mixer or in a large bowl with your hand mixer until fluffy and add eggs one at a time and beat until smooth. Sift the remaining dry ingredients together.
Mash bananas in a bowl with sour cream and vanilla. Add the dry ingredients and banana mixture alternately to the sugar and egg mixture in thirds, blending to combine each time, but trying not to overbeat.
Divide into two cake pans and bake 27-34 minutes, until a skewer in the center comes out clean. Cool on a rack completely before frosting.
Prepare the frosting: Blend melted chocolate with melted butter and vanilla. Sift the sugar and salt to remove lumps, then blend into chocolate butter mixture. It should look like wet sand.
Add 1 tablespoon of coffee milk at a time until you reach the right consistency, it should be thick and spreadable and you should be able to make good swirls. Leave at room temp until you frost the cake.