Beat cake mix, 1 egg, and butter with an electric mixer at medium speed until combined. Press mixture into the bottom of a lightly greased 13- x 9-inch baking dish.
Beat cream cheese and sugar with an electric mixer at medium speed until smooth. Add remaining 2 eggs, 1 at a time, beating well after each addition. Gradually add cocoa, beating until blended. Pour mixture evenly over chocolate layer.
Bake at 350° for 35 to 40 minutes or until a wooden pick inserted in center comes out clean. Cool. Cut into squares. Serve with mint chocolate-chip ice cream and chocolate sauce.