In a heavy bottomed pot saute onion with oil until translucent, then add ham hock, lima beans and chicken stock and cook over medium heat for 30 minutes, or until the lima beans are very soft. Puree in a food processor and strain through a fine sieve into another pot, bring to a boil and add corn, cream and crayfish tails. Bring to a boil again, add the fava beans, nutmeg and serve hot.
