Banana Chocolate Marble Cake

Cake: Preheat oven to 350 degrees. Grease a square baking pan. Combine flour and baking soda and mix well and set aside. Blend sugar and butter using electric mixer and scrape sides of bowl when necessary. Add sour cream, banana, egg and vanilla and beat until smooth. Add flour mixture and blend just until combined on low speed. Gently fold in melted chocolate and zest and stir just until marbled pattern develops. Do not overmix. Pour batter into baking pan. Bake 40-45 minutes or until toothpick inserted into center comes out clean. Cool in pan 15 minutes and invert onto rack. Cool to room temperature. Ganache: scald cream in saucepan and remove from heat. Add chocolate and zest. Stir until blended and cover pan. Set aside. After about 15 minutes, stir frosting until it is smooth and pour into a bowl. Chill until firm. Flip cake right side up onto a serving plate and frost with ganache. --