12tablespoonsunsalted butterat room temperature, cut into pieces
1cupheavy creamat room temperature
1tablespoonmaldon saltor any flaky sea salt
Add the sugar and corn syrup (if using) and heat over medium-high, whisking it as it begins to melt. Once the sugar is mostly melted, stop whisking and swirl the pan occasionally while the sugar cooks. Continue cooking and swirling until the sugar is reddish-brown and has a slight toasted aroma. If you are using an instant-read thermometer, you want it at 350 degrees F.
Once the caramel reaches 350 degrees, add the butter all at once and whisk until butter is completely melted. Turn off the heat and slowly pour the cream into the caramel. It’s going to bubble up again but just keep whisking. Whisk until all of the cream has been incorporated and the sauce is smooth. Add the salt and whisk to incorporate.
Let it cool, then use it or pour it into a jar and store it in the fridge. You will want to warm it up a bit once it’s chilled.
The corn syrup helps keep the sugar from crystalizing. It's not necessary, but I like to use it as an added insurance policy.