HEAT oven to 350°F Spray bottom only of a 13 x 9-inch pan with no-stick cooking spray. Combine all brownie ingredients in large bowl. Beat 50 strokes by hand. Spread in prepared pan. Bake 28 to 32 minutes or until set. Cool completely.
BEAT 1/2 cup butter and cream cheese in medium bowl until light and fluffy. Add remaining filling ingredients. Beat until smooth. Spread evenly over cooled brownies.
PLACE frosting ingredients in microwave-safe bowl. Microwave on HIGH (100% power) 30 seconds. Stir. Microwave an additional 10 to 15 seconds as needed until melted. Stir until smooth. Pour evenly over filling. Spread carefully to cover.
REFRIGERATE 1 hour before cutting into bars. Store in refrigerator.