For the brownies:
Preheat oven to 350º. Grease a 9 x 13" pan with nonstick cooking spray.
Chop the butter and the unsweetened chocolate into chunks and place together in a microwave safe bowl.
Microwave on low power in 30 second intervals, stirring in between until melted. (You could also melt them over low heat in a saucepan, stirring constantly). Set aside to cool, while stirring.
In a separate small bowl, combine the flour and baking powder. Stir the flour into the chocolate batter, just until combined. Don't over mix.
Pour batter into greased pan and bake for 20-30 minutes or until a toothpick inserted in the center comes out clean. Remove from oven and allow to cool completely.
For the Frosting:
Combine all frosting ingredients and beat until light and fluffy. Add more milk if you want it thinner.
Spread the frosting evenly over the cooled brownies. Refrigerate while you make the chocolate glaze.
For the Chocolate Glaze:
Place chocolate chips and butter in a microwave safe bowl. Microwave one low power in 30 seconds intervals, stirring in between, until melted and smooth. Allow to cool for about 5-10 minutes.
Spread evenly over the frosted brownies. Return to fridge to allow the chocolate to harden.
Allow the bars to sit in room temperature for 10 minutes before cutting into squares. (If you try to cut into them while they are cold the top chocolate layer will crack pretty easily and they won't be as pretty.)