In Heavy Saucepan, Over Low Heat, Melt Chips With Sweetened Condensed Milk And Salt. Remove From Heat; Stir In Walnuts And Vanilla. Spread Evenly Into Wax Paper-Lined 8 Or 9-Inch Square 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.