Heat oven to 350°F (325°F for dark or nonstick cookie sheets). Spray cookie sheets with cooking spray. In large bowl, beat cake mix, butter and eggs with electric mixer on low speed just until moistened. Stir in peanut butter pieces and peanuts.
Drop dough by rounded tablespoonfuls 2 inches apart onto cookie sheets.
Bake 7 to 10 minutes or until edges are set and tops appear dry. Cool 2 minutes; remove from cookie sheets. Cool completely. Store covered.