BBQ Baby Back Ribs with "Secret Sauce"

Name: BBQ Baby Back Ribs with "Secret Sauce"
Prep time: 15 min
Cook time: 3 h 35 min
Total time: 3 h 50 min
Cuisine: American
Ingredients: 1 cup brown sugar; 1 tablespoon kosher salt; 1 tablespoon dry mustard; 1/2 teaspoon black pepper; 2 tablespoons garlic powder; 2 teaspoons cayenne pepper; 1 tablespoon paprika; 10 pounds baby back pork ribs – also sold as “pork loin back ribs” (3 large racks); 1 cup yellow mustard; 1 cup apple cider vinegar; 2/3 cup ketchup; 3 cloves garlic, minced; 1/2 teaspoon freshly ground black pepper; 1 cup drippings from oven-cooked ribs (skim the fat before using)