Combine the pork, fat and crushed ice in a bowl and then, working quickly, use a meat grinder to grind the mixture through a medium die. Put the mixture in the freezer for 30 minutes and then grind again through a small die. (Preferably grind the meat mixture into a bowl set atop an ice bath to keep the meat cold.) Note: It is imperative that the meat be at a constant cold temperature so that the fat doesn't get too soft. You should be able to see clear definition between the lean meat the specks of fat in the ground mixture. Place ground meat in the bowl of a stand mixer fitted with a paddle attachment. Add all remaining ingredients except for the hog casings.
Mix the meat mixture with the paddle for 3-4 minutes until threads begin to appear in the meat: If you take a clump of meat and pull it apart with your fingers you will see tiny threads pulling apart. When you see this, your meat is ready.*
Place the meat mixture back in the refrigerator to chill while you prepare the casings.
Thread your sausage stuffer with the prepared hog casings, fill the sausage stuffer with the meat mixture, and stuff the casings being careful to avoid air gaps while also being careful to not over-stuff the casings.
Twist the sausages into links. Use a sausage pricker to prick any air bubbles out of the links. Makes about 20 links about 6-inches long.
For best results chill the sausages overnight. This will give the flavors time to develop.
To cook, gently poach the bangers in lightly salted water and then fry, grill, or bake them. Once poached they will keep in the fridge, tightly wrapped, for up to a week.