Prepare brownies according to directions using 13x9 pan. Only bake until almost done in the middle.

Using a nonstick saucepan for best results, slowly melt butter, add half & half and stir in cocoa with a spatula. Do not use milk. On low heat, slowly stir in confectioner's sugar until all is melted and completely smooth and a thick consistency that will spread or pour. Add another tablespoon or so of half & half if necessary for right consistency and add vanilla after removing from heat.

Pour over brownies and let the icing set.