Red Velvet Whoopie Pie "Cake"
Line bottoms of 2 (9-inch) round pans with waxed paper; lightly spray with cooking spray. Prepare cake batter as directed on package, stirring in melted chocolate and food coloring. Pour into prepared pans. Bake 22 to 25 min. or until toothpick inserted in centers comes out clean. Cool 10 min.; remove to wire racks. Cool completely. Prepare marshmallow mixture as directed. Place 1 cake layer, flat-side up, on cake stand; top evenly with marshmallow mixture. Top with remaining cake layer, flat-side down. Sprinkle with sugar before serving.
Bake the cakes up to 2 days ahead. Place cakes on a platter. Cover tightly with plastic wrap. Fill as directed when ready to use.
Use a #40 scoop to easily scoop cake batter onto baking sheets.