Cook the dried tagliatelle or noodles in a large pan of boiling salted water for about 6 minutes (but cook fresh for 2-3 minutes), until it is just tender but still firm, al dente.
Meanwhile, mix the butter with the cheese and milk in a heated serving dish and season to taste with salt and pepper. Drain the noodles thoroughly and add to the cheese mixture. Toss well until the noodles are coated. Serve immediately with a little extra grated cheese.