Blanch the trotters in boiling water, rinse them, and put in a large saucepan with all the vegetables and salt.
Bring to the boil, turn down the heat and simmer for 3 hours. Check from time to time to see they are always covered with water. Add some hot water if necessary.
To check if the trotters are cooked, carefully lift one out. If you can easily remove a bone, they are ready. If not, leave them longer.
For The Farce
Melt the butter over medium heat in a frying pan. Add the shallot and garlic, cook for a minute or two, then add the mushrooms.
Sauté until they are cooked through.
Add the parsley, season with salt and pepper.
Mix well, then transfer to a plate to cool.
Using a food processor, process the chicken breast with salt and pepper and the egg whites, one at a time. Slowly add the cream, then transfer to a bowl when blended.
Add the cooled mushrooms, mix well, cover with plastic film and keep refrigerated.
When the trotters are cooked, lift them onto a large plate. Keep the cooking broth.
Wait until the trotters are just cool enough to handle, then remove all the bones. Do not tear the skin, which must be in one piece.
Place each trotter in one piece on a double layer of dampened plastic wrap. Place a spoonful of the mushroom farce on to each boned trotter, and then roll up into their original shape, using the plastic wrap. Wrap them tightly, then twist both ends, and tie with kitchen string so they resemble a Christmas cracker.
Reheat the pork bouillon and simmer the wrapped trotters for 30 minutes.
The trotters can be prepared to this stage up to two days in advance. Keep refrigerated.
Remove the plastic wrap.
Put some of the braising liquid into a frying pan, let it reduce a little, then add the trotters and cook, turning frequently and basting them until they are hot and the surface is glazed.
Serve with sautéed mushrooms, mashed potatoes, or a simple green salad.