Line an 8-inch square pan as follows. Turn the pan over, cover with a 12-inch square of aluminum foil shiny side down, fold down the sides and corners to shape the foil, remove the foil, turn the pan over again, and place the foil into the pan, pressing it carefully to fit smooth. Set aside. In the large bowl of an electric mixer (or any large bowl, with a wooden spatula) mix the butter with the graham cracker crumbs, sugar, and peanut butter. Turn into the lined pan. With the bottom of a teaspoon smooth the mixture to make an even layer. Let stand at room temperature. Break up the chocolate and place it in the top of a small double boiler over hot water on low heat. Cover with a folded paper towel (to absorb steam) and the pot cover. Let stand for a few minutes until partly melted. Then uncover and stir until completely melted and smooth. Remove the top of the double boiler (dry its underside), and pour the chocolate onto the peanut butter layer. With the bottom of a teaspoon smooth the chocolate all over the bottom layer, touching the sides of the foil. Refrigerate for an hour (or longer, if you wish) until firm. Lift the candy from the pan by lifting the aluminum foil. Place the candy, still on the foil, on a cutting board. Fold down the sides of the foil and let stand. If you cut this into squares while it is cold it will crumble. Let it stand for about an hour, then cut into 32 small bars. Serve at room temperature. The taste will remind you of Reese's peanut butter cups. Recipe is from _Maida Heatter's Book of Great American Desserts_.