Preheat the grill to medium high.
Cook the pasta in a large saucepan of salted water until al dente – this will take approximately 5 minutes. Drain and reserve 250ml of the cooking water.
Add a little oil to a frying pan and cook the bacon until crispy.
Return the pasta to the saucepan with the reserved water, milk, blue cheese, two thirds of the hard cheese, the mustard, half the parsley, a little salt and the black pepper. Place over a high heat, bring to a boil, stirring until the sauce has warmed through and thickened.
Turn the mixture into a 1½ litre ovenproof dish. Mix together the breadcrumbs, walnuts, remaining cheese and parsley and sprinkle over. Place under the grill until golden and bubbling.
Serve with a salad of rocket leaves, sprouting peas and beans, sliced cucumber, chopped cherry tomatoes and sliced red onions. Add a dressing made with olive oil, Dijon-style mustard, lemon juice, salt and black pepper.