Chocolate Marshmallow Treats

Melt margarine in large saucepan over low heat. Add marshmallows and stir until completely melted. Remove from heat. Add rice krispies cereal. Stir until well coated. Using buttered spatula or waxed paper, press mixture evenly into buttered 15 ½" x 10 ½" pan. Set aside to cool. For filling, combine chocolate with shortening in small saucepan or in top section of double boiler. Stir over very low heat or over hot (not boiling) water, until morsels melt and mixture is smooth. Remove from heat. Cut cooled cereal mixture in half crosswise. Reserving about ⅓ cup of the melted chocolate mixture, spread remaining over one half. Top with other half, gently pressing halves together. Drizzle reserved chocolate over top. Chill just until chocolate is firm. Cut into 1 ½ inch squares. Store tightly covered at room temperature in cool, dry place.