Parboil the potatoes for 5 minutes, then drain and leave to cool. Slice each half into about 3 rounds.
Pre-heat oven 160 C / Gas 2-3. Mix dry mix sachet with the cold water and blend well.
Heat the oil in a wide casserole on medium heat; when hot, brown pork until coloured. Remove with a slotted spoon to a plate.
Add onions to same pan and fry until softened, then add garlic. Stir and cook for a minute, then add apple, parsnips and sweet potatoes. Crumble over chicken stock cube and add thyme and bay leaves. Stir well, then return pork with all the juices from the plate. Add the chicken chasseur mixture, mustard and salt and pepper.
Bring to the boil, stir and put lid on. Place in oven and cook for about 1 1/2 hours, or until pork is tender. Check halfway and stir.
Raise oven heat to 190 C / Gas 5.
Use the sliced potato to arrange on top of casserole, cook until potatoes are cooked through.
Before adding the potatoes, if gravy is too thin, sprinkle over some chicken gravy granules and stir through until you have the consistency you like. You can also add a drained tin of peas, if liked.