Heat the oven to 130C/260F/gas mark ½.
Heat a tablespoon of oil in a large casserole dish over medium heat.
Add the onion, carrot and celery, and start them cooking.
Once they are sizzling nicely, turn down the heat and let them sweat, stirring often, for a good 10 minutes.
Meanwhile, heat a tablespoon of oil in a large frying pan over medium-high heat.
Add a third to half the lamb (depending on the size of your pan), season and cook, stirring from time to time, until well browned.
Transfer to the veg pot and repeat with the remaining lamb, adding a little more oil if need be.
With the now empty frying pan over a moderate heat, deglaze with the cider, scraping up the brown bits stuck to the base.
Add this to the casserole with the mustard and herbs, pour in enough water barely to cover the meat and veg, bring to a simmer and transfer to the oven.
Cook until the meat is tender: about two hours, but start checking after an hour.
Season again to taste, then serve with creamy mash and lightly cooked greens.
Apple sauce or some lightly fried slices of apple are a very nice addition on the side.
