Begin by heating a large casserole pan over medium heat and adding 1 tablespoon of goose fat. Season the beef shin generously and fry it in batches until it develops a beautiful golden brown crust on all sides, about 3-5 minutes per batch. Turning the meat carefully ensures even browning, which intensifies flavor — add a little more goose fat if the pan dries out. As each batch finishes, transfer the browned beef to a colander placed over a bowl to catch any juices. In the same pan, now infused with the rich beef flavors, add the bacon, shallots or pearl onions, mushrooms, sliced garlic, and bouquet garni. Fry gently until everything is lightly golden, developing a fragrant base for the stew. Stir in the tomato purée and allow it to cook for a few minutes, blending seamlessly into the mixture; this deepens the sauce's richness beautifully. Return the browned beef and reserved juices to the pan, stirring thoroughly to combine. Pour over the red wine and add about 100ml of water, just enough to make the meat float without fully immersing it. Bring this to a gentle boil, then use a spoon to scrape up the caramelised bits from the pan's bottom — these little morsels pack a punch of flavor that will elevate your stew. Preheat your oven to 150°C (fan 130°C, gas mark 2). Create a cartouche by tearing off a piece of foil slightly larger than the pan, trimming as needed so it rests gently on the stew surface to keep moisture locked in while cooking. Pop the covered casserole into the oven and let it cook slow and low for 3 hours, allowing the beef to become tender and the flavors to meld. If you notice the sauce is too watery at the end of cooking, carefully remove the beef and vegetables with a slotted spoon and set aside. Increase the heat under the pan and simmer the sauce until it thickens to a luscious consistency, then return the meat and vegetables to absorb the intensified flavors. For the celeriac mash, peel and cube the celeriac. Heat 2 tablespoons of olive oil in a large frying pan over medium heat, then add the celeriac cubes. Fry them for about 5 minutes until they turn a lovely golden color, seasoning with salt and pepper to enhance their natural sweetness. Add sprigs of fresh rosemary, thyme, two bay leaves, and the cardamom pods to the pan, then pour in 200ml water, just enough to nearly cover the celeriac. Lower the heat and partially cover the pan, letting the celeriac gently simmer for 25 to 30 minutes until tender and most of the water has evaporated. Once soft, drain any remaining liquid and remove the herb sprigs, bay leaves, and cardamom pods. Lightly crush the celeriac with a potato masher to a rustic mash, then finish with a glug of olive oil and adjust seasoning to taste. To serve, spoon the hearty beef bourguignon into warm bowls and nestle a generous spoonful of the fragrant celeriac mash on top. Garnish with a bay leaf for a touch of elegance if desired. Enjoy this soul-warming meal paired with a glass of the same red wine used in cooking for a perfect harmony of flavors.