Spray a large loaf pan or 8-inch square baking dish with cooking spray.
Stir white sugar, 3/4 cup cream, corn syrup, butter, vinegar, and salt together in a heavy pot; bring to a boil. Stir in remaining cream. Cook, stirring constantly, until caramel is 244 degrees F (117 degrees C), or until a small amount of caramel dropped into cold water forms a firm but pliable ball, 10 to 20 minutes. Remove from heat and cool briefly.
Stir walnuts and vanilla extract into caramel; pour caramel into prepared baking dish. Cool completely, at least 1 hour. Turn baking dish over onto a flat work surface to remove cooled caramel from dish; cut caramel into serving pieces.