Bison Osso Buco Alla Milanese

1 1/2 cups all-purpose flour salt and freshly ground black pepper, to taste
6(1 1/2-pound) bison shanks, sawed crosswise into 2 pieces, or 6 (1 pound) large bottom parts of shank.
1/2 cp olive oil, or as needed divided
1/2 cup (1 stick) unsalted butter
2 large or 3 medium yellow onions
4 large carrots, peeled and chopped
4 celery stalks, chopped
2 cups dry white wine
2 cups beef broth
2 cups peeled, seeded, chopped plum tomatoes (fresh or canned), or canned tomato sauce (see cook's note)

GREMOLATA:
1 tablespoon minced garlic
2 tablespoons grated lemon zest (colored part only)
6 tablespoons chopped fresh flat-leaf parsley

1. For the osso buco, spread flour on plate and season with salt and pepper. Dust osso buco with seasoned flour, shaking off excess. In large, heavy skillet heat 1/4 cup olive oil over high heat. Add half of osso buco and brown on all sides (do not crowd in pan or it wll steam rather than brown), 10-15 minutes. Transfer to plate. Repeat with remaining osso buco, using remaining oil, or more if needed.
2. In large dutch oven, melt butter over medium heat. Add onions, carrots, and celery; cook until onions are pale gold, about 12 minutes. Place osso buco shanks, marrow-side up, on top of vegetables and add wine, broth and tomatoes or tomato sauce.
Bring to a gentle boil, reduce heat to low, cover and simmer until osso buco is very tender, 4 1/2-5 hours. Meat should be fork tender and almost falling off bones.
3. To thicken sauce, remove lid and boil over medium-high heat until reduced to desired consistency.
4. For gremolata, combine garlic, zest and parsley in small bowl. Sprinkle over shanks. Cook 5 minutes longer to give gremolata time to infuse into dish.

**COOK'S NOTES**
If you use diced tomatoes, the sauce will be lighter and brothier. If you use tomato sauce, the pan juices will be richer and will cling to the meat. Gremolata is a traditional mixture of lemon zest, garlic, parsley and sometimes anchovy that is added as a flavorful garnish after the osso buco has finished braising.