Preheat the oven: preheat the oven to 180°C / 350-375°F / Gas Mark 4-5.
Season: use kitchen tongs to place lamb onto chopping board in one flat layer. Season both sides with salt and pepper.
Sear: add olive oil to pan, turn heat to high, place lamb into the pan and sear for at least 3 minutes each side to brown the meat. Once browned, remove and transfer to a chopping board with layer of paper towel.
Vegetables: without rinsing the pan, add carrot, celery and onion, fry for 2 to 3 mins on high heat. Then add the garlic and thyme, stir to combine and allow to cook for a further 2 to 3mins.
Sauce: add the tomato paste and diced tomatoes to the pan. Crush the boullion cubes with your fingers and sprinkle over the combined tomato vegetable mixture. Turn the heat to low and allow the dish to simmer.
Lamb: use kitchen tongs to place the seared lamb back into the pan on top of the tomato vegetable mixture.
Stock and wine: pour in the wine, followed by the chicken stock. Place the bay leaves in the middle of the dish.
Bake: place a lid on the pan and transfer to the middle shelf in the oven. Cook for 1 hour 30 mins. You can remove during this time at 30 minute internals, place on a heatproof surface and use tongs to rotate the lamb to the other side.
Gremolata: add the chopped parsley, minced garlic and lemon zest to a small bowl and stir to combine.
Polenta: cook the polenta according to the packet instructions, add 2 teaspoons of butter and stir to combine.
Serve: portion the polenta onto plates. Place the lamb osso bucco onto a heatproof surface in the centre of the table and provide serving utensils.
Garnish: place the gremolata in a small bowl on the table for garnish, alternatively provide finely chopped parsley and cracked black pepper for serving. Enjoy!