Braised Short Rib French Dip

Name: Braised Short Rib French Dip
Ingredients: 1 tablespoon unsalted butter; 2 medium red onions, sliced; 2 ounces red wine; 2 tablespoons bacon fat; 3 celery stalks, rough chopped; 2 medium carrots, rough chopped; 2 medium red onions, rough chopped; 1 tablespoon tomato paste; 12 ounces Burgundy wine; 5 sprigs fresh thyme; 2 bay leaves; 2 sprigs fresh rosemary; 3 ounces peeled garlic; 32 ounces beef stock; 1 1/2 pounds boneless short ribs; Kosher salt and freshly ground black pepper; Vegetable oil, for cooking; 4 French sandwich rolls; 8 ounces Gruyere cheese, shredded; Serving suggestion: coleslaw