Preheat oven to 350 degrees.
Blend Margarine, Sugar and Cocoa in a large bowl. Beat in your eggs, one at a time then add in Salt, Vanilla and Flour. Mix l until a batter-like consistency.
Spread onto a 10x15x1 inch greased cookie sheet for approximately 25 minutes. Remove from oven and spread your bag of Marshmallows over the top.
Return then to the oven to bake for another 3 minutes or until Marshmallows are soft and puffy. Allow to Cool.
For your Chocolate Frosting:
Mix up 1 stick margarine (softened),
1/4 cup milk,
1-2 tsp vanilla,
3 tablespoons of cocoa, and
2-3 cups of powdered sugar in a medium bowl until desired consistency.
Spread over the top of the bars and voila! All Done! ;)