Easy Triple-Chocolate Fudge
["1 (14 oz.) can sweetened condensed milk", "2 Tbsp. butter or margarine", "16 oz. (2 2/3 c.) milk chocolate chips", "1 (3 oz.) bar bittersweet chocolate, coarsely chopped", "1 (3 oz.) bar white \"chocolate\", coarsely chopped", "1/2 c. coarsely chopped toasted walnuts"]
["Line an 8 or 9-inch square pan with foil or waxed paper, letting liner extend a few inches above pan on 2 sides.", "Stir condensed milk and butter in a medium-size saucepan over low heat until butter melts.", "Remove from heat; add chocolate chips and stir until melted and smooth.", "Stir in remaining ingredients. Spread in prepared pan and refrigerate 8 hours, or until firm enough to cut.", "Lift foil by ends onto cutting board.", "Cut fudge in 1-inch squares.", "Store airtight with waxed paper between layers."]
["condensed milk", "butter", "milk chocolate chips", "bittersweet chocolate", "chocolate", "walnuts"]