1Heat oven to 350°F. In large bowl, stir together cookie mix and flour. Add remaining cookie ingredients; stir until stiff dough forms.
2Shape dough into 28 (1 1/4-inch) balls; place 2 inches apart on ungreased cookie sheet. Flatten balls slightly with your hand.
3Bake 8 to 9 minutes or until set. Remove cookies from cookie sheet to cooling rack; cool completely.
4In small bowl, mix filling ingredients. For each whoopie pie, spread or pipe filling on bottom of 1 cookie. Top with second cookie, bottom side down; gently press together.