To prepare the cake: Preheat oven to 350°F Grease and flour two 9" cake pans. In the food processor, coarsely chop the candy bars; set aside.
In a large mixing bowl, cream the butter and sugar with an electric mixer. Beat in the eggs one at a time, scraping down the sides of the bowl after each addition. Mix in the mashed bananas and vanilla.
In a separate bowl, combine the flour, soda and salt. Add the dry ingredients and the buttermilk alternately to the egg mixture (in two to three additions each) and incorporate thoroughly. Fold in the chopped Butterfingers and divide the batter between the cake pans.
Bake for 30 minutes, or until a toothpick inserted in the center comes out clean. Cool the cakes on wire racks for 10 minutes. Invert onto a rack and cool completely before frosting.
To prepare the frosting: In a large mixing bowl, blend the cream cheese, butter and vanilla with an electric mixer until smooth, scraping down the sides of the bowl. Add the powdered sugar and peanut butter and mix until smooth.
To frost the cake, place one layer on a serving plate. Spread 1/4 of the frosting over the top. Place the second layer on top. Spread the remaining frosting over top and sides of the cake. Can garnish with additional crushed Butterfingers if desired!
Makes 10 servings.