Mince the lean pork and pork fat finely. Season generously with salt, pepper, and at least a pinch each of nutmeg, cloves, mace and thyme. Add the breadcrumbs and egg yolks and mix well. Refrigerate the mixture to make it easier to handle, then stuff into the skins and twist to secure the ends. If sausage skins are not available, coat with egg and dry breadcrumbs. Serve grilled or fried.