Place your grinder head, grinding plate (3/8-inch), and die in the freezer for 30 minutes. Meanwhile, cut the beef chuck, pork shoulder, and pork back fat into 1-inch cubes. Spread on a sheet pan and refrigerate until the meat reaches 34–36°F and fat pieces are firm at the edges but not frozen through, about 20 minutes.
1 lb pork shoulder (Boston butt), 0.5 lb pork back fat
In a small bowl, combine the Prague Powder #1, kosher salt, smoked paprika, black pepper, granulated garlic, cayenne, and dry mustard. Whisk thoroughly so the cure is evenly distributed through the spice blend — uneven cure distribution creates pockets without nitrite protection.
10 grams Prague Powder #1 (pink curing salt, 6.25% sodium nitrite), 28 grams kosher salt, 2 tablespoons smoked paprika, 1 tablespoon coarse-ground black pepper, 1 tablespoon granulated garlic, 1 teaspoon cayenne pepper, 1 teaspoon dry mustard powder
Grind the cold meat and fat mixture once through the chilled 3/8-inch plate into a large bowl set over an ice bath. Work quickly. If the grinder starts struggling or the fat begins to smear rather than cut cleanly, the meat is warming — stop and re-chill everything for 15 minutes before continuing.
1 lb pork shoulder (Boston butt), 0.5 lb pork back fat
Sprinkle the combined cure and spice mixture evenly over the ground meat. Add the ice water one tablespoon at a time. Mix by hand or with the paddle attachment of a stand mixer on low speed for 90 seconds, until the mixture becomes slightly tacky and the proteins begin to bind — the mix will pull away from the bowl in a cohesive mass. Do not overmix past 2 minutes; fat smearing risks rise sharply with time and temperature.
10 grams Prague Powder #1 (pink curing salt, 6.25% sodium nitrite), 28 grams kosher salt, 2 tablespoons smoked paprika, 1 tablespoon coarse-ground black pepper, 1 tablespoon granulated garlic, 1 teaspoon cayenne pepper, 1 teaspoon dry mustard powder, 0.25 cup ice water
Fry off a small test patty in a dry skillet over medium heat until cooked through. Taste for salt and seasoning balance. Adjust the remaining uncooked mixture if needed, remembering that smoke will add additional salt-adjacent flavor during cooking. Re-chill the bulk mixture to 36°F before stuffing.