Heat oven to 180C/160C fan/gas 4. Tip the duck into a large bowl and season. Scatter over the flour and toss until coated. Heat the oil in a large ovenproof casserole dish with a lid and spend a good 10 mins slowly browning the duck on all sides - try to get as much colour on it as possible. Remove the duck to a plate, then add the carrots, onion and garlic to the dish and cook for 5 mins until just starting to colour.
Nestle the duck amongst the veg and pour over the wine. Add the herbs, season, then bring everything to the boil. Cover with a lid and place in the oven, undisturbed, for 1½ hrs. Remove from the oven and leave to cool. Lift the duck into a container, strain the sauce into another and chill both. Can be made up to 2 days ahead or frozen for up to 3 months. Once chilled, lift the fat off the sauce and set aside for the Golden potatoes (see 'Goes well with').
To serve, heat the cleaned dish and sizzle the lardons for 5 mins. Turn up the heat, add the mushrooms and cook for 3-4 mins. Return the duck and sauce to the dish and simmer for 10 mins until the duck is heated through and the sauce has reduced a little. Serve each person a duck leg with some sauce spooned over, Golden potatoes and some green beans, if you like.