Pre-heat the oven to 180c.
Put an ovenproof pan on the hob on high heat. You'll want to make sure that pan has a lid, but that the lid isn't on right away.
If you're using tinned tomatoes, put half a tin into a pan and start them reducing now.
Season the lamb with salt and pepper.
Dust the meat with flour. You just want a thin, thorough coating all over. This will provide texture to the meat and will help to thicken the sauce once everything starts coming together.
Make sure the oil is hot enough and drop the meat into the pan, browning it all over.
Set the lamb aside and deglaze the pan with 300ml chicken stock. Let it simmer for a few moments and scrape the base of the pan, then pour that stock straight back into its container.
Re-oil the pan and get it back on the heat.
Finely chop the onion, celery and either carrot or pepper. Get them into the pan for a few minutes with some seasoning.
Add in some finely chopped garlic and allow a couple minutes more, then add the bay leaf and some thyme, or whatever herb you have handy.
Add the tomatoes and cook for a few minutes, then remove everything from the pan.
Slice half a leek into thin slices and give them a good wash, then fry on both sides at medium heat, allowing them to pick up a little bit of heat and a little bit of oil, but not taking them so far as to colour. Season as you go.
Put everything back into the pan, add any additional seasoning you wish to add and pop the lid on, then place in the oven for about 2 and a half hours. Ovens vary and cooking times can change, so keep an eye on it as you go. If you need to top up the liquid, add some stock or water.
Garnish with olive oil, parsley and lemon zest and serve either alone, with mash, greens or whatever you have available.