Heat the oven to 350 degrees. Coat an 8-inch baking pan with non-stick cooking spray.
Combine the brown sugar and 1/4 cup melted butter in a small bowl until blended; pour over the bottom of the baking pan. Arrange the sliced bananas over the caramel mixture.
Whisk the flour, baking powder, cinnamon, nutmeg, and allspice in a medium bowl. Beat 1 cup sugar and 6 tablespoons butter in a large bowl at medium speed for 2 minutes or until creamy. Beat in 1/2 cup of the sour cream. Beat in the egg and vanilla. Slowly beat in the flour mixture alternately with the milk, beginning and ending with the flour mixture.
Spoon and spread over the bananas. Bake for 40 to 45 minutes or until a toothpick inserted in the center of the cake comes out clean.
Cool in the pan on a wire rack for 5 minutes. Invert the cake onto a serving plate and cool completely.
Meanwhile, beat the heavy cream and 2 tablespoons sugar at medium-high speed until soft peaks form. Add 1/2 cup sour cream; beat until soft peaks form. Serve with the cake.