Cake
2 1/4 cups cake flour
1 teaspoon baking powder
1/2 teaspoon salt
1/8 cup (1 stick) unsalted butter, room temperature
1 1/2 cups granulated sugar
3 large eggs
1 tablespoon dark rum
1 teaspoon vanilla extract
3/4 cup sour cream
1 teaspoon baking soda
2 cups mashed ripe bananas (about 5)
1 1/2 cups chopped Butterfinger bars (about 6 ounce)

Position rack in top third of oven; preheat to 350 degrees F. Butter 2 (9-inch) diameter cake pans with 1 1/2-inch high sides. Line bottoms with wax paper rounds. Butter and flour paper.

Sift flour, baking powder and salt into medium bowl. Using electric mixer, beat butter in large bowl until fluffy. Gradually add sugar and beat 2 minutes. Add eggs 1 at a time, beating well after each addition. Beat in dark rum and vanilla extract.

Combine sour cream and baking soda in medium bowl. Add mashed bananas to sour cream mixture and stir until well blended. Add dry ingredients to butter mixture alternately with banana mixture, beginning and ending with dry ingredients. Stir in chopped Butterfingers.

Divide batter between prepared pans. Bake until center of cake feels firm and tester inserted into center comes out clean, about 30 minutes. Cool in pans on rack 10 minutes. Run small knife around sides of cakes to loosen. Turn out cakes onto racks and cook. Peel off wax paper. (Can be prepared 1 day ahead. Wrap cakes tightly and store at room temperature.)

Glaze
2/3 cup whipping cream
7 tablespoons unsalted butter, cut into large pieces
1 tablespoon light corn syrup
14 ounces semisweet chocolate, chopped
2 teaspoons dark rum
1 teaspoon vanilla extract
1 3/4 cups chopped Butterfinger bars (about 7.5 ounces)

Combine cream, butter and corn syrup in heavy medium saucepan. Bring to simmer over medium heat, stirring until butter melts. Remove from heat; add chocolate and stir until melted and smooth. Stir in rum and vanilla extract. Pour glaze into small bowl. Cover and refrigerate just until cool and thick, stirring occasionally, about 40 minutes.

Transfer 1 cake layer to platter. Slide wax paper strips under edges of cake. Stir glaze until smooth. Spread 1 cup glaze evenly over top of cake layer. Top with second cake layer. Spread remaining glaze over top and sides of cake. Cover top and sides of cake with chopped Butterfinger bars. Remove paper strips. (Can be made 2 days ahead. Cover cake and store at room temperature.)