1) Preheat oven to 350 degrees. Line a 9 x 13-inch pan with foil extends over the edges by at least one inch. lightly spray with nonstick cooking spray and set aside.
2) Chop both the unsweetened chocolate and butter into chunks and place together in a microwave-safe bowl. Microwave in 30 second intervals, stirring in between, until just melted and smooth. Set aside to cool, stirring occasionally.
3) With an electric mixer or stand mixer, beat eggs, sugar, and vanilla for 2 minutes. While the egg mixture is being beaten, measure out the flour and combine with the baking powder. While the mixer is running, slowly add the melted chocolate and beat to combine. Turn the beater speed to low and add in flour by spoonfuls. Mix just until combined. Pour batter into prepared pan and bake for 20-30 minutes or until knife poked in center comes out clean.
4) Cook completely on metal rack. When brownies have cooled to room temperature, prepare the frosting. Combine milk, powdered sugar, butter, peppermint extract, and food coloring. Start with 1 1/2 T milk, and beat until light and fluffy, add more milk by the teaspoon as needed. Spread frosting evenly over the brownies and then chill the brownies in the refridgerator.
5) While the brownies are chilling, prepare the chocolate glaze. Place chocolate chips and 6 T butter in a microwave safe bowl. Microwave in 30 second intervals, stirring in between, until just melted and smooth. Set aside to cool for about 15 minutes and then carefully spread on top of the frosting layer. Return the pan to fridge to cool.
6) When chocolate has hardened, use the edges of foil to remove the entire sheet of brownies from the pan. Cut into squares and serve.
7) Tip: You can substitute 1 teaspoon of other flavorings such as lemon, orange, cherry, strawberry, etc for the mint and then change the food coloring accordingly.
8) Christmas Candy Can Brownies:Use a few drops of red food coloring in the frosting layer and sprinkle crushed peppermint candy canes on the top for a festive holiday treat.