Preheat oven to 375°. Place Butterfinger candy bars in a food processor; process until ground. In a large bowl, cream butter and 2 cups ground candy bars until blended. Beat in eggs.
In another bowl, whisk flour, baking powder and salt; gradually beat into creamed mixture.
Shape into 1-in. balls; roll in remaining ground candy bars.
Place 2 in. apart on parchment-lined baking sheets.
Bake 8-10 minutes or until tops are cracked.
Immediately press a piece of candy into the center of each cookie.
Cool on pans 2 minutes. Remove to wire racks to cool.
Freeze option: Freeze cookies, layered between waxed paper, in freezer containers. To use, thaw before serving.