Preheat the oven to 350 F. In a large bowl, combine butter, powdered sugar, and peanut butter until fluffy. Add in vanilla extract, and mix until smooth.
Add in the flour mixture and mix until it is fully combined. Fold in the Reese's pieces candy. Roll the cookie dough into balls, and place onto a large ungreased baking sheet.
Bake for 10-12 minutes. Place the remaining 1/2 cup powdered sugar into a shallow dish. Roll the cookies into the powdered sugar. Let sit on a cooling rack to cool completely.
