In a large braiser or sauté pan, sauté the guanciale very gently in a small amount of olive oil until it has lightly browned and rendered most (but not all) of its fat. Remove and set aside until needed. Do not discard the rendered fat.

Meanwhile, bring a large pot of salted water to a boil. Throw in the fava beans and parboil them for about 3-5 minutes, depending on their size. Remove them with a slotted spoon and plunge them immediately into a bowl of ice water, then drain. Do not discard the cooking water.

Setting aside a few fava beans for garnish, place the rest in a blender along with the rendered guanciale fat, a small ladleful of your cooking water (enough to make the purée thick but pourable) and a pinch of salt.

Blend until perfectly smooth, then pour the resulting purée into the pan where you sautéed the guanciale. Keep warm over the barest flame while you cook the pasta.

Bring the water you cooked the fava beans in back to a boil and throw in your pasta. Cook until slightly under al dente.

Transfer the pasta with a skimmer to the pan with the fava bean purée. Turn on the flame and simmer the pasta, along with another ladleful of pasta water, in the purée for a minute or two, until the pasta is fully cooked and the purée coats the pasta nicely.

Off heat, add the grated cheese and toss well, adding a bit more of the cooking water if needed. Taste and adjust for seasoning.

Serve right away, topped with the guanciale and reserved fava beans.