Preheat oven to 350°. Beat first 4 ingredients at low speed with a heavy-duty electric stand mixer 20 seconds; increase speed to medium, and beat 1 minute. Pour batter into a greased and floured 13- x 9-inch pan.
Bake at 350° for 27 to 30 minutes or until a wooden pick inserted in center comes out clean. Cool cake in pan on a wire rack 10 minutes.
Bring sugar, milk, and butter to a boil in a heavy 2-qt. saucepan over medium-high heat, stirring occasionally; boil 1 minute. Remove from heat; stir in chocolate morsels until melted and smooth. Quickly spread frosting over warm cake. Cool completely (about 1 hour).
Note: For testing purposes only, we used Duncan Hines Moist Deluxe Devil's Food Cake Mix and Comstock Original Country Cherry Pie Filling or Topping.