1. For the osso bucco: Generously season meat with sea salt and pepper.
2. Add olive oil to dutch oven or deep cast iron pan. Sear meat on high heat for a few minutes per side. Remove meat from pan and set aside.
3. Peel and finely chop onion, carrot, and celery and sauté with garlic over medium heat until browned.
4. Add a little of the beef broth to deglaze the pan. Add tomato paste and stir.
5. Return meat to pan and add bay leaf and thyme. Add enough broth to cover meat most of the way (it doesn't have to be submerged).
6. Bring liquid to a boil, then reduce heat to a light simmer. Cover pan and leave the lid slightly ajar.
7. Simmer on low heat for 3-4 hours (or even more), until the meat is falling off the bone. Make sure beef is cooked through until an internal temperature of 145F is reached.
8. Remove meat and continue simmering the liquid, uncovered, until it has reduced into a sauce, about 15 minutes.
9. For the roasted radishes: Meanwhile, preheat oven to 400F. Remove radishes from stems, trim, and clean.
10. Place whole radishes in an oven-safe baking dish. Toss radishes with oil and sprinkle with sea salt.
11. Bake for 20-25 minutes (stirring halfway) or until radishes are tender.
12. For the gremolata: Meanwhile, zest the lemons. Mince parsley.
13. Mix all ingredients together.
14. Serve osso bucco and sauce garnished with gremolata alongisde roasted radishes.