Place all ingredients, except marshmallows in mixing bowl.
Blend at lowest speed, then beat at medium speed 2 minutes.
Spread batter in 10 x 6 in baking dish.
Microwave at 50% (Medium) 6 minutes.
Rotate 1/4 turn every 3 minutes.
Increase power to high.
Microwave 2-5 minutes until done.
Let stand directly on countertop 5-10 minutes.
Place marshmallows, cut side down and close together on cake after it has stood 3-4 minutes.
Cool cake and frost with Chocolate Frosting.
Cut between marshmallws.
Cake slices more easily if allowed stand several hours after frosting.
Frosting: In small mixing bowl, combine chociolate, butter and milk.
Microwave at 50% (Med.) 3-4 minutes or until chocolate is soft and mixture is thick, stirring after half the time.
Stir in remaining ingredients.
Let stand 5-10 minutes.
Beat until smooth and of spreading consistancy, 1-3 minutes.