I just used two boxes of brownie mix and cooked it in a jelly roll pan as directed.
Mint Frosting:
1/4 c softened butter
2 1/2 c powdered sugar
1 1/2 - 3 TBS milk
1/2 tsp peppermint extract
green food coloring
I doubled this recipe since I did the cookie sheet of brownies. To make the mint frosting, cream the butter and sugar. Add the milk 1 tbs at a time, beating until it is smooth and spreadable. Beat in peppermint extract and tint to desired shade with greeen food coloring. Frost the cooled brownies, cover, and chill 1 hour.
Chocolate Topping:
3/4 c semisweet chocolate chips
3 tbs butter
I doubled this recipe too...Pour chips into microwave safe bowl, add the butter, and microwave on high for 1 1/2 min or until chocolate melts. Stir until smooth. Pour the chocolate over the brownies and smooth it with a knife. Refrigerate for 45 minutes or until the coating hardens. Bring brownies to room temperature, then cut into pieces.