So here it is.
Brownie mix for 9x13 pan
Frosting - 3 c powdered sugar, 3 T cream, 6 T melted butter, 1 t peppermint extract (or to taste), green food coloring
Topping - 5 oz unsweetened chocolate, 6 T butter
Bake your favorite brownie mix according to package directions in a 9" x 13" pan. Cool completely.
For the frosting, mix together powdered sugar, cream, and melted butter. Add peppermint extract , a few drops at a time, until flavor is right. Tint pale green. Frost brownies when they have cooled. Refrigerate.
For the topping, melt together chocolate and butter. Pour over frosted brownies; tilt pan to spread topping over frosting evenly. Refrigerate until topping is solid. Cut into squares.