Combine sugar, cream and corn syrup in a large pan. Cook to soft ball stage on a candy thermometer.
Put 4 tablespoons butter on 2 large platters. Pour the candy onto the platters and let cool. While the candy is cooling, prepare a 9x13 pan by buttering the pan. Or you can line with foil and butter the foil. This makes for easier cutting of the candy once done.
Add vanilla and beat until creamy and it has lost it's glossy appearance, pour into the prepared pan and let set up.
Added nuts are optional.
NOTE: If you don't have a thermometer, you can drop a small amount of candy into a bowl of ice water. If it makes a soft ball that flattens when removed from the ice water, it is done.
There are more detailed instructions for candy in my "Mom's Fudge" recipe.