Soak the beans overnight in plenty of water, then drain. Put into a pan and cover with fresh water. Boil hard for 10 minutes. Reduce heat and simmer until tender about 45 to 60 minutes.Drain, reserving cooking water.
Put half the beans, together with half the onion and garlic, into a large, oven proof casserole. Add herbs, tied together with a piece of string. Bury two of the strips of lemon zest in the beans. Lay the ham knuckle on top, then cover with remaining beans, onions, garlic and lemon zest. Mix syrup, Tabasco and mustard and pour over. Season lightly with salt and pepper, then pour over just enough of the reserved cooking water to cover. Cover the casserole tightly and bake at 70ºC , 300 C, gas mark -20ºC or 3 hours. Arrange the apple pieces decoratively over the beans. You may not need them all. If there is rather too much liquid left in the dish, scoop a little more out so that the apples can perch more comfortably. Dot with butter and return to the oven for an hour. If using rum, pour it over the top just before serving.