Cube and chill the beef and beef fat, then chill them in the freezer for about 30 minutes, alongside your grinder apparatus.
Run the meat through the medium plate of your grinder into a bowl set into a larger bowl of ice.
Mix the seasonings, milk powder, and cure together in a small bowl.
Put the meat into the bowl of a stand mixer, and sprinkle on the cure/seasoning mix. Make sure the meat is still below 40°F (4°C).
Mix the meat with the paddle attachment, adding the water as you go, until it forms a sticky, fibrous mass that clings to the walls of the mixer and the paddle.
Stuff the meat into casings (not too tight or they will burst!) and twist it into links. Pop any bubbles in the casings with your Thermapen.
Allow the links to sit, uncovered, in the refrigerator overnight to cure and dry out just a little.
The next day, preheat your smoker to 180°F (82°C). Set up an air probe attached to your Smoke X to monitor the temperature. Put the sausages in the smoker, insert a needle probe into one of them, and close the lid. Set the high-temp alarm on your Smoke X2 meat channel to 160°F (71°C). Smoke the sausages until the high-temp alarm sounds on your meat channel. It should take a few hours.
Verify the internal temperature with your Thermapen ONE. If saving the sausages for later, plunge them into an ice bath to chill and stop cooking.
Otherwise, dig in and enjoy!