Prep and Cook the Lamb
Pre-heat your oven to 170°C; (338°F) for a fan oven or 190°C (374°F) for a standard oven. Cut your garlic cloves into thin slivers, and the rosemary into small spriglets.
Make slits all over the meat. Dab some anchovy paste into each slit, along with a sliver of garlic and a spriglet of rosemary. You can make anchovy paste by firmly rubbing over 4-5 anchovies with the back of a knife until they form a smooth paste - mix this with a bit of oil (it'll keep in a jar in the fridge for months).
Chop an onion, a carrot or two and a stick of celery into 1cm (about half an inch) slices and spread them in a single layer in the bottom of a roasting tin. Place the meat on top, and pour in boiling water up to the top of the vegetables. Place the roasting tin in the oven and roast for 7 minutes per 100 grams (3.5 ounces). This will give you medium-cooked meat. If you want it more cooked, give it 10 minutes per 100g. At the end of the cooking time, remove the meat from the tin, put it on a warmed plate and cover it tightly in aluminium foil. Let it rest for 20-30 minutes.
Make the Mint Sauce
While the meat is cooking, wash and finely chop the mint leaves. Put them in a jug and cover them with boiling water. Add salt, sugar and vinegar and stir well. When the sauce has cooled a little, and the flavours started to meld together, taste it and adjust the flavouring if required. Put the jug in the fridge until needed.
Make Roast Potatoes
Peel some potatoes and cut them into irregular-shaped chunks. Place into a pan of boiling salted water and cook for about 15 minutes until almost, but not quite, cooked. Drain the potatoes, put them in another roasting tin, cover them in oil and sprinkle on some chopped rosemary and a pinch of salt. You can put them in the oven with meat if you wish, or wait until it's done and give them 20-30 minutes at high heat. Turn them occasionally so they get crisped-up all over.
Make the Gravy
No roast dinner is complete without gravy. Most chefs and cookbooks tell you to simply stir some flour into the pan juices, but in my experience that only makes enough gravy for a not-very-hungry goblin. So what you really do is drain the juices from the roasting tin, add as much chicken stock as you like, simmer on low heat, and sift in some flour. Break up any lumps of flour that may form.
Carve the lamb into thick slices, serve with roast poatatoes, mint sauce, whatever steamed vegetables you fancy, possibly a Yorkshire pudding and lashings of gravy. Sit back and revel in the glory of a traditional British roast dinner.