An ancient member of the pea family (Europeans and North Africans have been eating them for millennia), fava beans have a nutty taste and buttery texture all their own.
Saute onion in olive oil. Season with salt. Stir in chicken stock. Bring to a simmer. Add fava beans. Simmer until tender. Stir in Parmesan. Puree. Season with lemon juice, salt, and pepper.