1Heat oven to 350°F. Line 2 cookie sheets with cooking parchment paper.
2In large bowl, beat butter with electric mixer on medium speed until creamy. Add cake mix, pudding mix, milk and eggs; beat on high speed until blended. Using 1 1/2-inch scoop, drop 24 slightly mounded scoops of dough about 1 inch apart onto cookie sheets.
3Bake 10 to 12 minutes or until set (do not overbake). Cool 2 minutes; remove from cookie sheets to cooling racks. Cool completely, about 20 minutes.
4For each whoopie pie, spread about 1 tablespoon frosting on bottom of 1 cookie. Top with second cookie, bottom side down; gently press together. Roll edges of whoopie pies in sprinkles.