In another small bowl, mix 1 tablespoon softened butter, 1 tablespoon cookie butter, the powdered sugar and milk until smooth. Spoon into small resealable food-storage plastic bag; partially seal bag. Cut off tiny corner of bag. Squeeze bag to pipe over top of bar. Cool completely, about 1 1/2 hours or until toppings are set. Cut into 6 rows by 4 rows.