13. Make sauce
To make the sauce, combine the reserved roasting juices with water, soy sauce, hoisin sauce, and sugar in a small saucepan over medium heat. While the sauce comes to a simmer, combine the tablespoon of cornstarch with the water to make the slurry. When the sauce comes to a simmer, stir in the slurry. Continue stirring until the slurry is well-integrated and has cooked through. The sauce should look glossy.