Divide the pound of beef into 8 equal portions. Gently press into 8 thin patties, about ¼” thick each.

Sprinkle each burger patty with a little salt.

Gently, dimple the center of each thin patty with your thumb.

Add a tablespoon of butter to the center of four of the patties.

Top the buttered patties with the remaining four patties and gently press the edges to seal.

Place the garlic butter burgers back in the fridge for 2 to 4 hours.

Prep your grill for a direct heat grilling. Clean and oil the grates. If adding woodchips, add them now. Nest the grill grates in place.

Close the grill and adjust the air vents to allow the grill to preheat to 450-500 degrees.

Add a small cast iron skillet or griddle to half of the grill to allow it to preheat until just smoking.

Add the onions to the dry griddle and allow them to start to caramelize for 2 to 3 minutes.

Add the butter on top and fold it in the onions as they cook, keeping a good eye on them to not burn them over the heat. When the onions are soft, golden, and translucent (6-9 minutes) transfer them and cover to keep warm.

Meanwhile, sprinkle the outside of the burger patties with salt and place them on the griddle. Cook for 2 to 4 minutes, flip, and cook 2 to 4 minutes longer to your desired internal temperature.

Because they have butter inside, it will melt and can cause flare-ups. Do not leave these unattended, and be prepared with a long spatula to flip and maneuver the burgers for even cooking.

Add the cheese during the last minute of cooking to melt.

Carefully transfer the cooked burgers to a platter to rest while you build the burgers.

Toast the buns, if desired.

Arrange the arugula on the bottom of the buns, then place a garlic butter burger on top.

Add the bacon and grilled onions.

Slather the top half of the bun with the roasted garlic aioli and place over top of the burger.

Serve immediately.