Using an electric beater, cream together the peanut butter and margarine until very soft and smooth. Beat in the powdered sugar until smooth, then beat in HALF the crumbs. Beat until well blended and moist. Mix in the remaining crumbs BY HAND. Spread the mixture in a 13 x 23 cm baking pan, patting evenly. Melt chocolate in top of double boiler over hot water or in microwave and pour over cracker mixture, Mark off desired size squares or bars and refrigerate PRFERRABLY overnight...if you keep out of them that long... Makes about 5 dozen...enjoy. This recipe from the LA Times California Cookbook.