Heat oven to 350°

Line 24 muffin cups with paper liners.

Beat cake mix, water, oil, and eggs in large bowl with electric mixer set aside on medium speed until moistened. Beat for 2 minutes. Divide evenly into muffin cups.

Bake for 18-22 minutes or until toothpick inserted in center comes out clean. Cool for 5 minutes. Remove from pan. Cool completely on wire rack.

Mix peanut butter and butter in medium bowl until smooth. Add powdered sugar and milk and beat until smooth and creamy.

Remove cupcakes from papers. Cut half crosswise using a serrated knife. Spread about 1 tablespoon filling on bottom halves. Frost top halves as desired with chocolate frosting. Place frosted tops over filling and press gently. Sprinkle with peanuts.