Microwave Mississippi Mud Cake

Ingredients:

1 c Butter
2 c White Sugar
4 Eggs
1/2 c Unsweetened Cocoa Powder
2 ts Vanilla
1^1/2 c All-Purpose Flour
1/4 c Chopped Walnuts
1/4 ts Salt
1/2 c Mini Marshmallows
1/2 c Butter
1/3 c Milk
1/4 c Cocoa Powder
1/2 ts Vanilla
4 c Confectioners Sugar

Directions:

-Put 1c Butter in large mixing bowl; melt
-Stir in 2c sugar and cocoa, add eggs and vanilla
-Beat until well blended
-Add flour, nuts, and salt
-Let rest for 10 minutes
-Pour into microwavable 11^3/4x7^1/2in. pan
-Microwave 12 minutes
-Make frosting with remaining ingredients
-Spread on cake
-Let stand until flat