Add granulated sugar and water (and optional corn syrup) to a medium sized, heavy duty sauce pan. Cook over medium heat, stirring frequently, until the sugar dissolves (3 to 5 minutes).
1 cup granulated sugar, 4 tablespoons water, 1 tablespoon corn syrup
Bring to a gentle boil while keeping the heat at medium, whisking or stirring frequently until sugar is dissolved.
Don't stir the caramel sauce at this point. Just gently swirl the mixture around the pan occasionally and brush down the sides of the pan with a wet silicone brush as needed to keep sugar crystals from forming.
Continue swirling and cooking until the mixture turns deep amber in color (6 to 9 minutes).
Remove from heat. Stir in the cream, butter, and salt until the butter has melted and the caramel is smooth. Be careful because the mixture will bubble up.
½ cup heavy cream, 5 tablespoons unsalted butter, ½ teaspoon sea salt
Stir in the vanilla extract at this point if you are using it.
1 teaspoon vanilla extract
Let the caramel sauce cool for 15 minutes in the sauce pan before pouring into a large glass jar for storage.