1. Preheat oven to 350 degrees.
2. Whisk together flour, brown sugar, sugar, baking soda and baking powder in a large mixing bowl.
3. Add butter, peanut butter, egg whites, vanilla, sour cream and milk and mix on medium speed until smooth.
4. Fold in mini reeses pieces and peanut butter chips.
5. Fill cupcake liners a little more than half way.
6. Bake 18-20 minutes.
7. Remove cupcakes from oven and allow to cool for 1-2 minutes, then remove to cooling rack to finish cooling.
8. While cupcakes cool, make icing. Mix butter and shortening together until smooth.
9. Add 2 cups of powdered sugar and mix until smooth.
10. Add peanut butter and 1 tbsp water, mix until smooth.
11. Add remaining powdered sugar and mix until smooth. Add additional water or milk until the right consistency.
12. Ice cupcakes and serve.
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