Burnt Onion Steak Sauce Recipe | Tasting Table

Name: Burnt Onion Steak Sauce Recipe | Tasting Table
Ingredients: One 3-inch piece orange zest; One 3-inch piece lemon zest; Half a large yellow onion, whole; 1½ sticks unsalted butter; 2 cups beef stock; 1¼ cups raisins; ¾ cup tomato paste; ¾ cup Champagne vinegar; 7 tablespoons Worcestershire sauce; ¼ cup capers; 3½ tablespoons gochujang; 3 tablespoons caper juice; 3 tablespoons balsamic vinegar; 3 tablespoons barley malt syrup; 1 tablespoon soy sauce; 1 tablespoon colatura (Italian anchovy sauce); 2 teaspoons celery seeds, toasted; 1 large red grapefruit, supremed