Japanese knotweed spears pushing out of the Bronx ground in early April.
Four cupfuls knotweed, chopped up as a bed for the lamb.
A handful of field garlic bulbs. Season both with some salt.
The lamb leg, drizzled with one lemon's juice, seasoned with salt and pepper, and spiked at the blunt end with slivers of regular garlic.
Roast at 350'F/180'C for 15 minutes to the pound (500gr) - for medium rare (add a cup of water to the pan before it goes in the oven). Cover with a lid or with foil for the first hour, then expose to the dry heat of the oven.
Rest for at least 15 minutes, afterwards. Scrape up the knotweed and arrange with the lamb in its (the lamb's) juices on a serving platter.
I made a potato gratin to go with the lamb, cooked in a skillet in the oven for an hour. It, too, was spiked with matchsticks of garlic and a little butter and cooked in enough water to cover. But in its last half hour I added some cream, which is absorbed and leaves a stickily delicious crust on the top layer of potatoes.
(If you can't find knotweed, use a lot of spinach, a mountain of spinach, and some sorrel - or much lemon juice. Roast the lamb on top. The spinach will disappear.)