Heat a skillet and ad oil, thyme and garlic. Stir- fry for a minute then, fold leek, pancetta and mushroom in.
Cook for about 5 min or until cooked through, then season to taste and remove from the heat.
Boil the pasta in plenty of lightly salted boiling water for 7 min. Reserve about 1/2 cup of the water, then drain the pasta.
Return the reserved water to the pan and add vegetable stock, whisk in the crème fraîche, then season to taste.
Stir in the drained pasta, mushroom and bacon, and half the parmesan cheese, mixing until melted.
Heat the grill for 3 mins. Tip the pasta and vegetables into a shallow, ovenproof dish or into mini casserole dishes.
Mix together the remaining Parmesan and thyme, then scatter on top.
Stand the dish on the base of a grill pan and grill for about 3 mins or until golden on top.
Remove and leave to stand for 5 mins before serving.