Halve the leeks lengthways and cut at an angle into 1/2-inch slices. Heat a wide saucepan, add a splash of oil and a knob of butter, and when you hear a gentle sizzling add the sliced garlic, thyme leaves and leeks. Move the leeks around so every piece gets coated. Pour in the wine, season with pepper and stir in the stock. Cover the leeks with the slices of Parma ham, place a lid on the pan and cook gently for 25 to 30 minutes. Once the leeks are tender, take the pan off the heat.
Whiz the mushrooms and bread with a pinch of salt and pepper in a food processor until the mixture looks like bread crumbs. Heat a generous glug of olive oil in a frying pan. Add the garlic cloves and the rosemary and cook for a minute, then fry the bread crumbs in the oil until golden and crisp. Keep shaking the pan - don't let the bread crumbs catch on the bottom. Drain on paper towels, discard the rosemary and garlic and allow the bread crumbs to cool.
Bring a big pan of salted water to the boil. Lay the lasagne sheets on a clean working surface and sprinkle with a little flour. Place the sheets on top of each other and slice into 1/2-inch strips. Toss through your fingers to shake out the pappardelle, then cook in the boiling water 2 minutes or until al dente.
Remove the Parma ham from the saucepan, slice up and stir back into the leeks. Season to taste with salt and pepper, then stir in the Parmesan and the rest of the butter. Drain the pasta, reserving a little of the cooking water, and add the pasta to the leeks. Add a little of the cooking water if need be, to give you a silky, smooth sauce. Serve quickly, sprinkled with some pangrattato, extra Parmesan and any leftover thyme tips. Serve the rest of the pangrattato in a bowl on the side.
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Recipe Excerpted from JAMIE AT HOME by Jamie Oliver. Copyright (c) 2008. Published in the U.S. by Hyperion. All Rights Reserved. www.jamieoliver.com