Pa's Fudge

Mix sugar, cocoa, milk, corn syrup, and salt in a large, heavy saucepan or Dutch oven. Place over medium heat and stir faithfully until sugar is melted. Bring to boil and cook to soft-ball stage (234 ° Fahrenheit). Stir occasionally to prevent sticking and scorching. Remove from heat and add butter and vanilla. Let cool to 110 ° without stirring. While the fudge is cooling, butter the bottom and sides of an 8-inch square pan. Beat the fudge with a wooden spoon until it becomes very thick and loses its gloss. Quickly pour into the prepared pan. Score while warm into 1-inch squares, then allow to cool thoroughly for several hours or overnight. Cut with a sharp knife when cool, dipping the knife into hot water between cuts if necessary. Store the fudge between layers of waxed paper in a sealed container in a cool place.