1. Butter a 13×9-inch (quarter sheet) pan and line with parchment paper.

2. In the bowl of an electric mixer, fitted with the paddle attachment, beat 1 ¼ cups peanut butter on speed 2 (medium) until creamy. Add butter and continue beating until creamy. Scrape down sides and bottom of bowl and gradually beat in 1 cup powdered sugar.

3. With hands or a wooden spoon, work in 1 cup powdered sugar and graham cracker crumbs.

4. Press down into prepared pan and smooth the top with spatula.

5. In a small saucepan, melt ¾ cup of peanut butter and chocolate chunks over low heat, stirring constantly until smooth.

6. Carefully pour melted chocolate over the graham cracker crust.

7. Refrigerate for at least 1 hour or until chocolate is firm. Cover with plastic wrap and store in refrigerator.

8. Cut into 12 bars.