Heat the oven to 140ºC.
Melt the goose/duck fat in a heavy pan/casserole dish with a close fitting lid.
Season the grouse and pork well with the salt and pepper.
Add the meat to the melted fat, along with the bay leaves, ensuring it is submerged and cover with the lid.
Place in the oven for 3-3½ hours until the meat is completely tender and falling from the bone.
Wait until it is cool enough to handle, then pick all the meat from the bones and place in a bowl.
Scrunch and shred the meat with clean hands, you want a slightly stringy texture.
Separate the fat from the juices lying at the bottom of the dish.
Mix in all the juices and half the fat along with the nutmeg and truffle paste.
Check for seasoning, then press into a non metallic dish/jar.
Cover with a thin layer of the remaining duck fat to seal in the truffle aroma (keep the rest for roast potatoes).
The rillettes are ready to eat, but will improve after a few days in the fridge, and will keep for at least a month in the fridge.