Preheat oven to 350°. Beat egg whites until stiff. Fold in egg yolks. Gradually add sugar, then flour and vanilla. In a separate bowl, melt the butter and add cocoa to it. Mix then add to egg mixture. Put in greased and floured 9x13 inch pan or a little bigger pan. Bake for 20 minutes. Cool. For Frosting - mix sugar, butter and milk together in a pan on the stove. Cook until bubbly. Then low boil for 1 minute and 30 seconds. Remove from heat and add marshmallows. Stir until melted. Add chocolate chips and stir until melted. Cool a few minutes then frost the brownies.