Heat 4 tablespoons of the oil in a saucepan, add the onions and garlic, and cook over medium heat until the onions are soft but not brown. Add the thyme, bay leaves, peppercorns, and salt, and pour the vinegar and water over. Bring to a boil and simmer for 20 minutes.
While the marinade is cooking, roll the eel pieces in the seasoned flour. Heat the remaining oil in a frying pan and cook the eel over medium heat for 15 minutes, turning frequently, until golden brown.
Transfer the eels to a glass or earthenware dish and pour the marinade over. Cool and then marinate in the refrigerator for at least 24 hours. Serve the eel pieces moistened with a little of the marinade.
© 1999 Jennifer Paterson and Clarissa Dickson Wright estate. All rights reserved.