Heat some olive oil and a knob of butter, add 3 of the chopped garlic cloves, some of the thyme and the leeks and coat in the oil. Add the white wine and cook out the alcohol. Add salt and pepper to taste.
Cover the leeks with the Parma ham and cook for 30 minutes.
Blitz the mushrooms and the bread to form breadcrumbs. In a frying pan, heat some olive oil, the last of the garlic (crushed) and the rosemary. Add the breadcrumbs and cook until golden and crisp.
Cook the pappardelle pasta in boiling salted water until tender with a bite at the centre, about 2 minutes.
When the leeks are tender, remove the Parma ham and slice thinly and add back to the leeks. Add the remaining butter with the pasta and a bit of pasta water; mix and serve immediately. Top with the breadcrumbs.