Place peanut butter, butter and marshmallows in large saucepan; cook on medium-low heat 5 to 7 minutes or until marshmallows are completely melted and mixture is well blended, stirring constantly.
Place 6 of the chocolate grahams on wax paper-covered baking sheet.
Spread evenly with the marshmallow mixture, using about 1/4 cup of the marshmallow mixture on each graham. Top with remaining 6 grahams to make sandwiches.
Cut crosswise in half. (You will have12 sandwich squares.)
Melt chocolate in small saucepan on low heat, stirring constantly. Dip sandwiches in chocolate, coating about half of each sandwich. Return to baking sheet. Refrigerate 20 to 30 minutes or until chocolate is set.
