Cool meat before grinding (this will help with the grinding).
Grind meat twice, once with the big adapter, then with the smaller one. This will avoid squishing the meat and the juice out of it (Hmmm... meat juice).
Mix the three types of meat together.
Cut onions in rings, cook until caramelized (TBD: add instructions).
Make 6 to 10 oz meat patties.
Salt meat on both sides before cooking.
Let meat come to room temperature before cooking. (Warn children and old people of imminent death).
Warm griddle to 400 F.
Cook meat patties 3-4 minutes each side.
Put cheese on meat and cover with lid. Put water under lid. Remove when cheese melted.
Put butter on the buns and cook them on the griddle.
Assemble burger: meat with cheese, onions and buns.