You can use mutton or lamb for this dish. Sadly, mutton still isn't a regular item in butchers and supermarkets, but it is the best meat for slow cooking by far, as it has that rich, almost gamey, flavour. Beer is great for cooking with as it doesn't impart that acidic flavour that wine does if it's not reduced correctly. I would suggest using a bitter, IPA, or a decent light beer for this.
8 x 70-80g mutton chump or neck chops (not too fatty)
Salt and freshly ground black pepper
A little vegetable or corn oil for frying
1 onion, peeled, halved and finely chopped
30g flour, plus a little extra for dusting
1tsp tomato purée
400-500ml beef or lamb stock
A few sprigs of thyme
150g small young carrots, peeled
Season and lightly flour the chops, heat some vegetable oil in a heavy frying pan and brown them on both sides. Melt the butter, reserving a little for the carrots, in a pan large enough to hold the chops. Gently cook the onion for 2-3 minutes until soft, then stir in the flour and cook for a minute on a low heat.
Add the tomato purée then gradually whisk in the beer, bring to the boil and continue boiling until it has reduced by half. Add the beef stock and thyme, season, cover with a lid and cook on a low heat for about 1-1 hours or until the chops are tender; top up with more stock or beer if it's getting dry. It's difficult to put an exact time on mutton so it will need to be checked during cooking.
Remove the chops from the sauce and simmer the sauce until it has thickened. Meanwhile, cook the carrots in boiling salted water with a little sugar until tender, then drain and toss in the remaining butter and season. Reheat the chops in the sauce, then serve on individual plates, or one larger serving plate, with the carrots scattered over.