Beat 1 1/4 cups peanut butter and butter in large mixer bowl until creamy. Gradually beat in 1 cup powdered sugar. With hands or wooden spoon, work in remaining powdered sugar, graham cracker crumbs and 1/2 cup morsels. Press evenly into prepared baking pan. Smooth top with spatula.
Melt remaining peanut butter and remaining morsels in medium, heavy-duty saucepan over lowest possible heat, stirring constantly, until smooth. Spread over graham cracker crust in pan. Refrigerate for at least 1 hour or until chocolate is firm; cut into bars. Store in refrigerator.