Heat oven to 350°F. Spray bottom only of 13x9-inch pan with cooking spray. In large bowl, stir cookie base ingredients until soft dough forms. Press dough in bottom of pan. Bake 12 to 15 minutes or until light golden brown. Cool completely, about 30 minutes.
In large bowl, beat all filling ingredients except powdered sugar with electric mixer on medium speed until creamy and smooth. Gradually beat in powdered sugar until well blended (filling will be thick). Press filling over cookie base. Refrigerate while preparing caramel layer.
In 2-quart saucepan, heat caramels and 2 tablespoons water over low heat, stirring constantly, until caramels are melted. Stir in peanuts. Spread evenly over filling. Refrigerate about 15 minutes or until caramel layer is firm.
In small microwavable bowl, microwave chocolate chips uncovered on High 1 to 2 minutes, stirring once, until melted. Spread evenly over caramel layer. Refrigerate about 1 hour or until chocolate is set. For bars, cut into 9 rows by 4 rows. Store covered at room temperature.