Beef Ribs with Orange BBQ Sauce

Name: Beef Ribs with Orange BBQ Sauce
Ingredients: 3 racks center-cut beef ribs (8 or 9 pounds total); 1 sweet onion, peeled and cut into 1/4-inch rings; 6 fresh thyme sprigs; 2 teaspoons fennel seeds; 1/4 cup kosher salt; 1/4 cup dark brown sugar; 1/4 cup cracked mustard seed; 1/2 cup paprika; 2 tablespoons freshly ground black pepper; 2 tablespoons cayenne pepper; 1/4 cup granulated garlic; Orange BBQ Sauce, recipe follows; 1 cup ketchup; 1/4 cup apple cider vinegar; 1/4 cup molasses; 1 cup orange juice; 1 tablespoon onion powder; 2 garlic cloves, minced; 1 teaspoon honey; 2 tablespoons Worcestershire sauce; 1 tablespoon balsamic vinegar; 2 tablespoons orange marmalade; 1 teaspoon dried red pepper flakes