4 cups granulated sugar
2 tablespoons light corn syrup
4 cups (1 quart) heavy cream, at room temperature
4 ounces (1/2 cup) unsalted butter, softened and cut into pieces
1/4 teaspoon table salt

Sugar can burn easily, so use a heavy-based pot; preferable one that doesn't have a dark interior so that you can monitor the sugar once it begins to color. Set a small dish of water and a pastry brush by the stove. Pour 1 cup water into a heavy-based 8 quart saucepan or dutch oven. Add the sugar and corn syrup. Cook over high heat, stirring often with a wooden spoon, until the mixture is clear and comes to a boil. If sugar crystals form on the sides of the pan, wash them down with a wet pastry brush.

Reduce the heat to maintain a gently boil; it shouldn't be spattering. Don't stir but check frequently while boiling gently until the sugar begins to turn a light honey color in spots, about 20 minutes. Whenever sugar crystals form on the sides of the pan, wash them down with a wet pastry brush. Swirl the pan gently to even out the color. When the mixture reaches a rich, red-brown color, about another 8 minutes, take the pan off the heat. Slowly pour in the cream (be careful - the mixture will bubble vigorously and produce a lot of steam). Stir with a wooden spoon, making sure any solidified caramel on the pan bottom or sides melts. (If it doesn't, set the pan over medium-low heat and stir gently until the caramel is completely smooth.) Stir in the butter and salt. Let cool to room temperature before stirring in the flavorings (if using) and pouring into individual jars.

For easy cleaning, soak the pot and utensils in hot water. To loosen any cooked-on sugar, fill the pot with water and set it on the heat.