Boil 1 can sweetened condensed milk in unopened can for 2 hours being careful to keep the can covered with water. Open can and blend the milk with 1/4 lb. butter, 1 cup sugar and 2 cups corn syrup. Boil slowly for 15 to 20 minutes in a heavy saucepan or skillet, stirring constantly until mixture reaches 250 degrees. Pour into flat buttered pan. Chill and cut into squares. Wrap pieces in waxed paper.