LINE 8- or 9-inch square baking pan with foil.
COMBINE morsels and sweetened condensed milk in medium, heavy-duty saucepan. Warm over lowest possible heat, stirring until smooth. Remove from heat; stir in nuts and vanilla extract.
SPREAD evenly into prepared baking pan. Refrigerate for 2 hours or until firm. Lift from pan; remove foil. Cut into 48 pieces.