Preheat oven to 350°.

Add peanut butter, butter and water to a saucepan. Cook over medium heat, stirring to combine until butter is melted. Remove from heat.

In a large mixing bowl, combine flour, sugar, brown sugar, baking soda and salt.

Pour peanut butter mixture into flour mixture and stir to combine.

In a small bowl, mix buttermilk, eggs and vegetable oil.

Pour into peanut butter batter and stir until well combined.

Spray a 10 x 15 inch jelly roll pan with non-stick cooking spray.

Pour batter into pan, spreading evenly.

Cook for 20- 25 minutes or until a toothpick inserted comes out clean.

Cool completely on a wire rack before adding the frosting.

Make the frosting by adding cream cheese and butter to a mixer bowl and beating with the wire whisk attachment for 2 minutes.

Add vanilla and mix until combined.

Next, add the powdered sugar and milk. Beat at low speed until combined and raise to medium speed, beating until fluffy.

Chop the Butterfingers and reserve 1/2 cup for garnish.

Fold the chopped candy bars into the frosting.

Spread evenly over the cooled cake and garnish with reserved Butterfingers.

Slice and serve or chill until ready to serve.