Cook the pasta in salted boiling water until al dente, then drain, reserving a little of the cooking water.
Meanwhile, cook a little of the butter in a frying pan until it foams then fry the bread until it is golden brown all over. Tip into a bowl and wipe out the pan. Add the rest of the butter and heat it until it foams and starts to brown. Add the chilli flakes and plenty of black pepper and cook for 1 min.
Tip the pasta back into the pan along with a splash of the cooking water and the cheese and toss together thoroughly. Sprinkle on the fried bread and toss everything together again.