Remove an oven rack from the oven, then oil well with a little oil and a piece of kitchen towel.
Puncture the leg of lamb all over with a small sharp knife.
Break and insert slices of garlic into the puncture holes.
Drizzle over the olive oil, and rub in well then season well with salt and pepper, then place the lamb on the oven rack.
Place the potatoes into a large baking tray that fits the bottom of the oven perfectly.
Season well with salt and pepper, add the rosemary also, and mix well.
Place the potato tray on the bottom rack in the oven.
Place the lamb into the oven above the potatoes making sure all the cooking juices fall into the tray below.
Shut the oven door and cook for 1 hour, turning the potatoes occasionally, so the juices from the lamb impregnate the potatoes. The potatoes should be cooked at the same time as the lamb, if not then, add a few more minutes. Taste and re season if needed.
After 1 hour 20-30 minutes, remove the lamb oven, wrap in foil and leave to rest for 30 minutes in a warm place, this will give you a perfectly cooked, pink leg of lamb.
Meanwhile bring a large pan of salted water to the boil,
One by one place all the vegetables, re-boil for 1 minute, then drain well.
Heat olive oil in a large wok, add the onions and garlic and cook for 3 minutes until they take a little colour, add the rest of the vegetables and the tomato puree/water mix and cook for 20 minutes until well reduced and cooked through, stirring well.
Once cooked add the fresh tomatoes and basil and just warm through, season well and add more extra virgin olive oil if needed.
Serve with the slices leg of lamb, mint hollandaise and potatoes.