Beat 1 1/4 cups peanut butter and butter in large mixer bowl until creamy. Gradually beat in 1 cup powdered sugar.
Mix in the remaining powdered sugar, graham cracker crumbs and 1/2 cup chocolate chips.
Press evenly into greased 13 x 9-inch baking pan.
Smooth top with spatula.
Melt remaining peanut butter and remaining chocolate chips in medium, heavy-duty saucepan over lowest possible heat, stirring constantly, until smooth.
Spread over graham cracker crust in pan.
Chill for at least 1 hour or until chocolate is firm; cut into bars. Store in refrigerator.