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. *If the meat mixture is too dry and stiff, add a little more ice water. You want a soft/smooth mixture that will easily go into the casings.*This is also the time to taste your sausage mixture so you can adjust the seasonings if needed. To do this, take a bit of the meat mixture, fry it up in a pan, taste it and adjust the seasonings if needed.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.For best results chill the sausages overnight. This will give the flavors time to develop. Makes about 20 6-inch links.
To cook, gently poach the bangers in lightly salted water and then fry or grill them. Once poached they will keep in the fridge, tightly wrapped, for up to a week. (See note for freezing instructions.)
To Freeze the Bangers: You can either freeze the Bangers raw prior to poaching (then thaw, poach, fry/grill) or freeze them after they're poached. Either way, lay the bangers out on a tray and place it in the freezer. Once frozen place the bangers in a ziplock freezer bag or airtight container. They will keep for up to 3 months.**VARIATION: To experiment I've added 3/4 cup of very finely chopped English Pub-Style Pickled Onions to these bangers and they were fabulous!