Heat oven to 350°F. Grease bottom only of 13x9-inch pan with cooking spray or shortening. (For easier cutting, line pan with foil, then grease foil on bottom only of pan.)
In medium bowl, stir brownie mix, water, oil and eggs until well blended (I added about a 1/2 cup of mini chocolate chips to the batter.) Spread in pan. Bake 28 to 30 minutes or until toothpick inserted 2 inches from side of pan comes out almost clean. Cool completely, about 1 hour.
In medium bowl, beat filling ingredients with electric mixer on medium speed until smooth. Spread mixture evenly over brownie base.
In small microwavable bowl, microwave topping ingredients uncovered on High 30 to 60 seconds; stir until smooth. Cool 10 minutes; spread over filling. Refrigerate about 30 minutes or until set. For brownies, cut into 9 rows by 4 rows. Store covered in refrigerator.