Preheat the oven to 350 degrees F. Cover the bottom of a 13x9 inch pan with cooking spray, then line with parchment paper and extend the paper over the sides of the pan. (This way, you can easily lift out the whole pan of brownies). Combine all the ingredients together in one bowl, stir until smooth. Spread into the prepared pan, and bake for 28-32 minutes or until done. Cool completely.
Meanwhile, beat together the 1/2 cup butter and cream cheese together in a medium bowl until light and fluffy. Add the remaining ingredients. Spread evenly over the cooled brownies.
Place the frosting ingredients in a microwave safe bowl. Microwave on high for 30 seconds, stir, then microwave again for 10-15 seconds as needed until the chocolate is melted. Stir until smooth. Pour evenly over the filling, and gently spread to cover the filling.
Refrigerate for at least 1 hour before cutting into bars. Store in the refrigerator.