Cake: 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: 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.)