Place cake mix in a bowl; cut in butter until crumbly. Press 2-1/2 cups into a greased 13-in. x 9-in. x 2-in. baking pan. Bake at 350 degrees F for 10 minutes; immediately sprinkle with chocolate chips. Drop frosting by tablespoonfuls over the chips. Stir milk into the remaining crumb mixture; drop by teaspoonfuls over top.
Bake 25-30 minutes longer or until bubbly around the edges and top is cracked. Cool on a wire rack. Refrigerate for 4 hours before cutting.
