The day before making the soup, soak the dried beans in cold water overnight. The next day, drain them and cook in boiling water for 40 minutes until tender, then drain and set aside.
While the beans are cooking, put the chicken and the remaining stock ingredients in a stockpot, bring to the boil then reduce to a simmer, uncovered, for 1 hour.
Remove the chicken from the stock and strain the stock. Pour the stock back into the pot and let it simmer until reduced to 2 litres.
Heat the olive oil in a big saucepan and sauté the garlic, then add the parsnip, cabbage and beans and sauté for a few minutes. Add the stock and bring to the boil. Skin the chicken and shred the meat off the bones.
Save half the meat for another use, then add the other half to the soup, seasoning to taste with salt and pepper. Add the chervil and parsley and let it simmer for 2 minutes before serving.