Shell the fava beans and blanch in boiling salted water for 2 minutes. Drain and, when cool enough to handle, slip off the tough outer skin of the beans. Discard skins and reserve beans on the side.

Heat a large pot of salted water to a boil and cook the fettuccine, stirring often, until al dente.

While the pasta is cooking, heat the olive oil in a large skillet over medium-high heat. Add the onion and pancetta and cook until the onion is soft and the pancetta begins to crisp, about 7 minutes. Add the garlic and cook for 1 minute. Add the favas and escarole to the pancetta and cook until the beans are tender, about 5 minutes. When the pasta is al dente, drain, reserving 3/4 cup of the cooking liquid. Add the pasta, reserved cooking liquid, and heavy cream to the fava mixture and cook, tossing to mix thoroughly, until everything is heated through. Season to taste with salt and freshly ground black pepper. Garnish with 2 tablespoons grated Pecorino Romano and serve immediately. Pass the extra grated cheese at the table.