Grind the pork and pork fat using the medium blade of a meat grinder.
Place both the pork and the fat in a large deep bowl. Add the onion, parsley, garlic, chiles, cayenne pepper, black pepper, thyme, allspice, saltpeter and salt. Beat vigorously with a wooden spoon until the mixture comes together and is smooth and fluffy.
Wash the casings under cold water to remove all traces of the dalt that they were packed in. Make sure to run water through the casings to clean the inside also.
Tie a knot about inches from the end of the casing and slide over the horn of a sausage stuffer.
Fill the casing until there is an inch of empty casing remaining and slip off the horn and tie into a knot. do not stuff casing too tightly or it could burst during the cooking process.
You can cook them right away or they will keep in the fridge for 5 or 6 days.
To cook, prick the casing with a knife in 5 or 6 places and coil into a 12" skillet and cover with water. Bring to a simmer over moderate heat and cook 30 to 40 minutes. The water will evaporate and there will be a small amount of fat lefft in the pan. Continue to cook 10 minutes, turn half way through to brown both sides.
NOTE: If you do not have a grinder you can ask the butcher to grind the pork and the fat for you. If you do not have a sausage stuffer, you can form the mixture into logs aproximately 2" in diameter and wrap tightly in foil or plasrtic wrap and refridgerate until ready to use. To cook, slice into 1/2" slices and fry them in a small amount of vegetable oil.