Heat enough oil in a large saucepan. Peel and thinly slice the onions. Fry, stir, and don't let them burn.
While the onions are softening, roll the lamb/mutton pieces in the flour, and add them in batches to the pot to brown. They must be well covered with flour, which helps the sauce thicken as you proceed.
Add more oil if necessary, and don't crowd the meat: take out the browned pieces and onion with a slotted spoon, and keep on a plate, then do the rest.
When all the meat has been browned, pour off all extra fat and oil.
Put the meat chunks and onions back into the pot.
The number of tomatoes is a case of: check to see if you think they are enough. If fat and huge, 6 - 8 might just be right. If your tomatoes are small, you'll need considerably more. The most important thing is that they should be vine-ripened and flavourful.
Skin the tomatoes. Use any method you like: I simply use a sharp serrated-edge knife or a small sharp peeling knife and peel them as thinly as possible.
Cut them into the pot (on medium heat), juices and all. Add the salt, Worcestershire sauce, sugar and pepper. Stir well.
Now: watch the pot for a while. The tomatoes should provide enough liquid -- do NOT add water to this dish, rather an extra tomato.
Then turn heat down, put lid on at an angle to allow steam to escape, and simmer gently for about 35 minutes.
Then add quartered peeled potatoes, if you feel like it.
Simmer gently until potatoes and meat are tender but not falling apart. Add the garlic towards the end of cooking.
Your finished dish should be a deep reddish brown and the tomatoes should have reduced to a thick sauce. There mustn't be a lot of liquid. If there is, turn up the heat, stir well, and let the extra liquid evaporate. You never add water to this stew (bredie) unless it threatens to burn.
Serve with the lemon rind and parsley strewn over the dish. This is always served with white rice. (And, naturally, maybe two fresh veggies and a green salad).
NOTE: the added sugar is very important. I would have preferred to say "1 tablespoon", but this is a matter of taste. The final taste of the dish should not be acidic.