Cube the pork into 2-inch chunks. Place in a freezer-safe container or bag. Leave in the freezer for about 20 minutes so that it firms up a bit. This will make it much easier for the pork to move through the grinder.
Grind the pork using a meat grinder into a large bowl.
In a food processor, pulse to finely mince the ham and garlic. Add mixture to the pork.
Add salt, sugar, and potato starch. Get your hands in there and mix thoroughly.
You will need (2) 9x5x3 loaf pans. Pack one pan with the pork mixture. Cover with foil.
Center the loaf pan in a 13x9 baking pan. To create a water bath, fill the large pan three-quarters of the way with water.
Bake for 2 hours or until the internal temperature reaches at least 155º F when finished.
The loaf will be swimming in a lot of fat. Discard the accumulated fat.
Cover the pan with foil again. Nest the empty loaf pan on top of the loaf. Place weights in the pan. I used my 3-pound dumbbells. Best use of those of those weights since I bought them last year. The weights will press the loaf.
Refrigerate the loaf overnight...with the weights.
Unwrap and store in an air-tight bag or container for a few days in the refrigerator. Unlike the canned version, it does have a shelf-life. :-) You can also freeze the ham loaf to enjoy later - wrap the loaf tightly with plastic wrap, zip into a Ziploc-like freezer bag, and store in the freezer for up to 3 months. When ready to eat, thaw overnight in the refrigerator.
Notes
You can substitute 2 pounds of ground pork for the pork shoulder to save time (thanks to a tip by an Instagram follower) or if you don't have a meat grinder. If you're using ground pork, you can skip steps 2 and 3.