First, put pasta shells on to boil in plenty of salted water. Fry sliced chestnut mushrooms in butter until nicely browned and set aside.
Add a little olive oil to the pan and fry thinly-sliced smoked pancetta, cut into 3-4 cm pieces, until crispy, then add a sliced banana shallot
and crushed clove of garlic, frying until softened. Return the mushrooms to the pan, season well with freshly-ground black pepper then tip in
a small glass of dry white wine and a handful of defrosted frozen peas (you can easily defrost these by putting in a sieve and running hot water
through them!). Bring to a boil and simmer for a few minutes, to drive off the alcohol. Then stir in a couple of Tbs of crème fraîche.
When the pasta is cooked, drain (saving some of the cooking water) and stir into the mushrooms and pancetta. Stir gently over a low heat
to mix well, adding a splash of the pasta cooking water if needed, to coat everything with the sauce. Serve garnished with chopped parsley.