Line 9-inch square pan with foil, with ends of foil extending over sides; spray with cooking spray. Microwave 10 oz. chocolate, butter and coffee in large microwaveable bowl on HIGH 2 min. or until butter is melted. Stir until chocolate is completely melted and mixture is well blended. Add brown sugar and eggs; mix well. Stir in combined flour and baking powder; pour into prepared pan.