You will need a flameproof casserole dish of approximately 2.25 litre capacity.
You need to start this recipe by soaking the beans. You can do this by covering the beans with twice their volume of cold water, then soaking them overnight. Alternatively, on the same day, boil them for 10 minutes then leave them to soak for a minimum of 2 hours.
Pre-heat the oven to 140C/gas 1. To cook the lamb, trim off any really excess fat and then cut it into rounds about 2cm thick. Now place the casserole over direct heat, add 1 tablespoon of oil, then, as soon as it's smoking hot, brown the pieces of meat, a few at a time, wiping them first with kitchen paper so that they're absolutely dry when they hit the fat (don't add more than 6 pieces at a time). Then as soon as each piece is nicely browned on both sides, remove the fillets to a plate and carry on until all the meat is browned.
Next, add the other tablespoon of oil and, keeping the heat high, brown the onions round the edges, moving them around until they take on a nice dark caramel colour - this will take about 5 minutes - then add the garlic, stir that into the onions and let it cook for another minute or so.
Now sprinkle in the flour and give it all a good stir, allowing the flour to soak into the juices. Add thyme leaves, then gradually add the stock, stirring all the while as you pour it in. Next, return the meat to the casserole and season it well with freshly milled black pepper, but no salt at this stage.
After that, drain the beans, discarding their soaking water, and add them to the casserole as well. Finally, add the thyme sprigs and bay leaves and, as soon as everything has come up to simmering point, place a tight-fitting lid on and transfer the casserole to the centre shelf of the oven to cook for 11/2 hours.
Towards the end of that time pour boiling water over the tomatoes and then, after 30 seconds, drain off the water and slip the skins off. Add these to the casserole, along with a good seasoning of salt, then replace the lid and carry on cooking for a further hour.
Before serving, remove the bay leaves and sprigs of thyme and taste to check the seasoning.
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