Mix first 4 ingredients by hand with spatula until well-blended. Turn into greased, floured 9 X 13 inch baking pan. Bake at 350 F 25-30 minutes, or until cake tests done. Let cool and cut into squares before adding icing. To make icing, combine sugar, butter and milk in saucepan. Bring to a boil, stirring constantly, and boil 1 minute. Remove from heat and add chocolate chips. Stir until melted. Pour over cake and spread.