In a shallow bowl, combine the flour, 1 tsp salt, and ½ tsp pepper. In a lidded Dutch oven, heat oil over medium-high heat. Dredge the Osso Bucco in the flour mixture, then, working in batches, sear in the oil, turning until all sides are brown. Transfer to a plate.
Add onions and cook over medium-high heat until they begin to soften, about 3 minutes, then stir in the garlic and pancetta. Continue cooking until the garlic softens and the pancetta begins to render, about 3 minutes. Stir in tomato paste and stir until it begins to darken, about 1minute. Add the wine and bring to a boil, scraping up all the delicious brown bits on the bottom and sides of the pot. Stir in the broth and bring to a boil.
Return the Osso Bucco to the pot with any accumulated juices. Add the carrots, celery, and thyme. Cover and cook over very low heat for 2 ½ hours until the meat is tender. Turn off the heat and let the pot sit undisturbed for 5 minutes so the fat can settle on top, then skim it off. Check the seasoning. Yum.