Rinse the beans and put them in a pan with the potatoes on top. Cover them with water. Bring to a boil and cook for about 60 minutes, untill they are soft, then drain them. At this point, the true fava bean purist will hold the pot between their legs and vigorously beat the beans with a wooden spoon while slow drizzling in the oilve oil.
The more modern method is to use a hand held whisk or even a potato masher to throughly puree the beans and potatoes, season with salt and pepper, then add the olive oil while stirring with a wooden spoon.