Heat the olive oil and butter in a pan. Fry the onions and pancetta in it. Add tomatoes and reduce to puree over medium heat for 8 to 10 minutes. Season to taste with salt and peperoncini. In the meantime, cook the maccheroni in plenty of boiling salted water until firm to the bite, drain and drain well. Mix with the tomato sauce, season well with pepper and mix with half of the pecorino. Arrange in deep plates and serve sprinkled with the remaining pecorino cheese and basil leaves.