For the ossobuco, peel and chop the onions and garlic. Clean or peel, wash and chop the carrots and celery. Heat 4 tablespoons of oil in a large frying pan. Fry the carrots, celery, onions and garlic until slightly browned.
Stir in tomato paste and sweat briefly. Remove the roaster from the stove and set aside.
Wash the meat, dab dry and prepare. Season with salt and pepper. Turn in flour and tap off the excess flour. In a large frying pan, heat 6 tbsp. oil in portions. Fry the meat in portions on both sides over medium heat for about 3 minutes until golden brown.
Remove the meat and place it on the roasted vegetables in the roaster.
Carefully drain the oil from the pan and deglaze the remaining roast with wine. Then bring to the boil until it has dissolved and reduce to about 1/4. Preheat the oven (electric cooker: 175°C/circulating air: 150°C/gas: see
Wash and quarter the tomatoes. Wash parsley, shake dry and chop coarsely with stalks. Pour beef stock into the wine stock. Add parsley, thyme and bay leaf, bring to the boil once. Season with salt and pepper.
Pour the sauce with the tomatoes over the meat, place the lid on top. Braise in the oven for 2-3 hours until the meat is tender. Meanwhile, pour your own roast stock over the meat about every 30 minutes.
For the puree, peel the celery tubers, dice them coarsely and cook them covered with laurel in salted water for about 20 minutes until soft. Wash the lemon, dab dry and finely grate the peel. Squeeze the lemon.
Drain the celery and warm the milk. Pour half to the celery and mash briefly with a hand blender. Gradually stir in the rest of the milk until the puree is creamy. Stir in butter and crème fraîche.
Season with salt, pepper, nutmeg, lemon zest and juice.
Remove the osso buco with the tomatoes. Pour the roast stock through a fine sieve into a pot. Bring the sauce to the boil and reduce for about 5 minutes. Season to taste with salt and pepper. Arrange the ossobuco with the tomatoes and the sauce.
Sprinkle Gremolata over it. Add the celery puree.