Preheat oven to 350°.
Cream 3/4 cup sugar and margarine at medium speed of a mixer until light and fluffy. Add egg and 1 egg white; beat well.
Add flour and cocoa to creamed mixture; beat well. Add vanilla; beat well. Pour into a 9-inch square baking pan coated with cooking spray; set aside.
Beat cream cheese and 1/4 cup sugar at high speed of a mixer until smooth. Add 1 egg white; beat well. Pour cream cheese mixture over chocolate mixture; swirl together using the tip of a knife to marble.
Bake at 350° for 30 minutes or until done. Cool completely on a wire rack.