1) Heat the oven to 170 C, 150 C fan, 325 F, gas 3. 2) Melt half of the butter in an oven proof casserole and brown half of the pork, about 10 minutes. 3) Remove the meat from the pan set aside 4) Repeat with the rest of the butter and pork. 5) Meanwhile, in another pan, dry-fry the lardons until crisp. Remove and set aside. 6) Add the shallots to the pan and fry with the onion and celery for a few minutes, to soften slightly. 7) Add the pork back to the casserole along with the lardons, onions and celery. Season to taste. 8) Add the mushrooms then pour over the cider and chicken stock to cover. 9) Cover the dish and cook in the oven for 2 hours until the pork is tender. 10) Add the crème fraîche, cornflour mix, mustard and tarragon to the casserole. Heat on the hob and stir until the sauce has thickened slightly.