Fry the bacon and leeks in the oil for 10 mins until the bacon is golden and the leeks soft. Tip in the peas and heat through. Meanwhile, boil the pasta and heat the grill to high.
Reserve 150ml of the cooking water before you drain the pasta, then add it, the soft cheese, half the grated cheese and the mustard to the pan with the veg. Stir until the cheese melts into a creamy sauce. Stir in most of the basil and the pasta, then scatter with the rest of the cheese. Grill for 2-3 mins until the cheese melts. Scatter with basil to serve.
