Mix 2-12 oz. pkgs. milk chocolate chips with 1 can sweetened condensed milk and 3 TB butter. Microwave for 3 minutes. Stir until well blended and it is smooth and shiny. Add a sprinkle of salt and 1 tsp. vanilla. Mix well. Pour into a buttered 8x8 pan. Chill until firm. Cut into 1 inch squares.