For Cake: Position rack in top third of oven; preheat to 350 degrees F.
Butter and flour two 9-inch cake pans with 1 1/2-inch sides.
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 Butterfinger bars.
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.
For 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.