Line a 8-or 9-inch square baking pan with waxed paper. In heavy, medium-sized saucepan, over low heat,melt all chips, with sweetened condensed milk, marshmallows and salt; stir until smooth and well blended. Rem,ove from heat, stir in nuts and vanilla. Spread evenly into prepared pan. chill 2 hours, or until firm. Turn fudge onto cutting board, peel off paper and cut into squares. Store loosely covered at room temperature. Makes about 2 pounds.