Mix all the meatball ingredients thoroughly; I season the meat with 1 tablespoon grated Parmesan, 2 tablespoons basil and 1 smallish garlic clove, as well as salt and pepper. Flour your hands and shape the mixture into about 32 small balls. Fry in batches in a non-stick pan for 5 minutes or more until golden and cooked right through. Shake the pan frequently so the meatballs keep in good shape and cook evenly. Transfer to a casserole and keep hot. Slice the mushrooms thickly, saute' them well and add them to the meatballs. Then "wash out" the frying pan with the chicken stock. Make a smooth rich sauce with the butter, flour, stock and cream. Add any juices that have collected in the casserole and simmer for several minutes. Away from the heat, season with salt and pepper, 2 tablespoons Parmesan and 1 heaped teaspoon Dijon mustard. Pour the sauce over the meatballs, cover and keep hot in a low oven. The mixture can be kept hot for some time without spoiling, or it can be prepared ahead and reheated close to serving. Boil the pasta until al dente and drain well. Add it to the casserole together with a small handful of fresh herbs -about 2 tablespoons each basil and chives, and 1 of parsley -and toss gently to mix well. Garnish with more basil, and serve with an undressed salad.