The apple sauce can be made ahead by peeling the apples, and cooking them with a few teaspoons of sugar and some water, for about 15 minutes, or until they are "mushy".
Chop the potatoes up into small pieces and boil them for about 1 - 2 minutes so that they are slightly cooked.
Meanwhile chop up an onion.
Discard water, pat dry potatoes, and heat the duck fat in a large pan. Do this about 15 minutes before the duck is ready to be carved.
Add the onions first, and then the potatoes, making sure they are in one layer only or some will not be cooked. You may have to do them in two batches depending on the size of your frypan.
Cook, undisturbed until the bottoms are brown and then mix and cook another 3 or 4 minutes till they are browned all over. You MAY have to add a bit more duck fat. Just before serving, chop up some parsley and sprinkle on top.
If you are making beans as I did, cook the beans a few minutes before the meat is being carved.
For the duck
Defrost several days ahead of time in the fridge.
Clean out the inside thoroughly, take of any bits of feathers as are often left on a duck, take off the big pieces of fat, and wash and dry thoroughly. Leave it in the fridge uncovered for several hours or overnight as this dries out the skin and helps it to go brown.
Score the duck by cutting in diagonal lines all over the skin, being careful to cut the skin only and not the meat. This ensures that the meat is not fatty as all the fat runs out.
Cut the lemons up, and rub lemon all over the duck. Rub some salt and massage it into the skin and also rub a bit of salt inside the duck.
Preheat the oven to 150°/130° fan forced - as it is very low, this will not take long.
Place the cut lemons inside the cavity of the duck.
Make sure the wing tips are tucked under the duck as these will burn otherwise.
Put the duck on a rack, with the breast side up - I used one that I use to cool biscuits on, spray the rack with a bit of olive oil so it does not stick, and put in the oven.
Bake for an hour, and take out.
Turn the duck carefully around, and put back in the oven for another 55 minutes, making sure again that the wing tips are pushed under the duck.
Take out and repeat so that the breast side is facing up again, and cook for 55 minutes.
Turn the heat up to 220°/200° fan forced and put the duck back in for up to 10 minutes just to crisp the skin up - I found I only had to put it in for a few minutes as the skin was already crisp.
Take out of the oven, let stand for a few minutes before carving - it will be so tender, you will come back for more!
Eat with the apple sauce, the fried potatoes, and beans, or you could bake some vegetables, though you would not put them in till about the last hour.
If you are making a chicken, cut these times in half or even less - you will be able to see when it is done.