1Heat oven to 350°F. Spray bottom of 13x9-inch pan with cooking spray.
2In large bowl, stir all Cookie Base ingredients until soft dough forms. Press dough in bottom of pan using floured fingers. Bake 15 to 18 minutes or until golden brown. Cool completely, about 1 hour.
3In small bowl, beat all Filling ingredients with electric mixer on medium speed until smooth. Spread mixture evenly over cookie base.
4In microwavable bowl, microwave all Frosting ingredients on High 30 seconds; stir until smooth. Cool 10 minutes; spread over filling. Refrigerate 30 minutes or until set. For bars, cut into 9 rows by 4 rows.