In a bowl, combine the dry cake mix, eggs and oil. With floured hands, press two-thirds of the mixture into a greased 13 x 9 inch baking pan. Set remaining cake mixture aside.
In a microwave-safe bowl, combine the milk, chocolate chips and butter. Microwave, uncovered, on high for 45 seconds, stir. Microwave 45-60 seconds longer or until chips and butter are melted. Stir until smooth.
Pour over crust. Drop teaspoonfuls of remaining cake mixture over top.
Bake at 350º for 20-25 minutes or until lightly browned. Cool before cutting
Makes 3 dozen