Spray a flameproof casserole pan with oil, add the onion and cook over low heat for 10 minutes. Add the garlic, potatoes, turnip and butter beans and stir to combine.
Add all the remaining ingredients, season to taste and bring to a simmer.
Transfer the casserole to in a preheated oven, 180°C (350°), Gas Mark 4, and cook for 45 minutes. Check the seasoning, remove the bay leaf and sprinkle with chopped parsley. Serve with a green salad, if liked.