Caramelized onions are super easy, but they take a long time to caramelize properly, so you want to start with them. Cut your onion into strips; heat the butter over medium-high heat in a skillet on the stove.
Once it’s melted, add your onions, stir into the butter and cook for 10 minutes, stirring occasionally.
After 10 minutes, turn down the heat to medium or medium-low. Stir every so often to make sure the onions aren’t burning. It’ll take 30 to 45 minutes more for them to brown. If you don’t have an hour, they’ll still be sweet, if not fully caramelized; the longer you can leave them, the better.
After you start your onions, cut the fat off of your rib-eye and cut the rest of the meat into 1- to 2-inch chunks. Put both in a bowl in the freezer for 20 minutes. You don’t want it to freeze, but you want it to harden so that it’s easier to grind.
After 20 minutes, take ½ of your rib-eye and fat and grind it in your food processor using pulses. Check it often, scraping down the sides with a spatula. Rib-eye can be chewy if not completely ground, so go a little further than you think you need to. Because you had it in the freezer, it shouldn’t goop together, but you’ll want to make sure it’s thoroughly broken up.
Start your mushrooms. Toss your mushrooms and balsamic vinegar in a skillet over medium heat on the stove. Cook until the mushrooms are tender. If the vinegar starts to cook off before the mushrooms are done, you can add some water or put a lid on the skillet to help steam them.
You can also add salt, pepper, or garlic to the mushrooms to give them an extra flavor of their own.
Time to heat your grill and start making your patties. Mix your ground rib-eye with salt, pepper, and blue cheese. Form into 6 equal balls and then squish into patties.
Grill until they’re as done as you like them.
To serve: top with onions and mushrooms and an extra dab of blue cheese if you’d like. I had hamburger buns available for my non-Primal guests, but I enjoyed one of these all on its own.