Preheat your oven to 350°F (175°C) and line a muffin pan with cupcake liners.

In a mixing bowl, cream together the sugar, brown sugar, and unsalted butter until the mixture is light and fluffy.

Mix in the peanut butter, sour cream, and vanilla extract until well combined.

Add the egg whites one at a time, mixing well after each addition.

In another bowl, whisk together the flour, baking powder, and salt. Gradually add this dry mixture to the peanut butter mixture, alternating with the milk and water.

Fold in the crushed Butterfingers.

Divide the batter into the cupcake liners, filling each about 2/3 full.

Bake for 20 minutes or until a toothpick comes out clean. Allow the cupcakes to cool completely.

To make the chocolate ganache, heat the heavy whipping cream until just boiling. Pour it over the chocolate chips, let it sit for a minute, then stir until smooth.

For the frosting, beat together the salted butter, peanut butter, and shortening until fluffy. Gradually add the powdered sugar and enough water or milk to reach your desired consistency. Stir in the crushed Butterfingers.

Frost the cooled cupcakes with the peanut butter frosting, then drizzle with chocolate ganache.