this is here as an aide memoire for me, really - I can never remember how long to cook lamb.
pre-heat oven to gas 8. Make a mulch of some olive oil, rosemary leaves, sea salt and black pepper, and spread it on the baa lamb. I also slung a glass or so of red wine in the pan, which is not per Nigel's instructions, but then a recipe is just a guideline to me, and it gives you something to make gravy with.
20 minutes as gas 8, then down to gas 6, and 15 minutes per 500g. This gives very pink lamb, so if you like yours more cooked, you'd better do it longer.
serve with potatoes roasted in goose fat, and leeks poached in chicken stock. And onion sauce. Lovely.