Chocolate Chip Cookie Surprise Cake

1 package yellow cake mix
1 cup whole milk
1/2 cup butter, melted
3 eggs
1 pouch chocolate chip cookie mix
1/2 cup firm butter or margarine, softened
1 egg
1 tub Creamy chocolate ready-to-spread frosting

Heat oven to 350 degrees. Generously grease bottom only of jelly roll pan, 15 1/2x10 1/2x1 inch, with shortening; lightly flour.

Beat cake mix, milk, melted butter and 3 eggs in large bowl with electric mixer on low speed 30 seconds; beat on medium speed 2 minutes. Pour into pan.

Make cookie mix as directed on package using softened butter and 1 egg. Drop dough by teaspoonfuls evenly over batter in pan.

Bake 35 to 40 minutes or until toothpick inserted in center comes out clean. Run knife around side of pan to loosen cake. Cool completely, about 1 hour. Spread frosting over top of cake. Store loosely covered at room temperature.

Makes 15 servings