HEAT oven to 350°F.
PREPARE cake batter as directed on package; set aside. Beat cream cheese, 6 Tbsp. peanut butter, egg and sugar with whisk until blended.
SPOON 2 Tbsp. cake batter into each of 24 paper-lined muffin cups; top each with 1-1/2 tsp. cream cheese mixture and 1 cookie. Cover with remaining cake batter.
BAKE 22 min. or until toothpick inserted in centres comes out clean. Cool cupcakes in pans 5 min.; remove from pans to wire racks. Cool completely.
STIR remaining peanut butter into Cool Whip with whisk until blended. Spread over cupcakes. Top with remaining cookies just before serving.