Cut both ends off one onion, then peel off the skin. Cut onion in half, then slice as thinly as possible. Repeat process with remaining onions, then set aside the sliced onions.

Measure out the balsamic vinegar and set aside.

Measure out the brown sugar and set aside.

Heat olive oil in a large skillet over medium heat, making sure the oil evenly coats the bottom of the pan. Add sliced onions to the pan, the liberally sprinkle with salt and pepper. Carefully stir ingredients together, then cook for about 20 minutes, stirring occasionally, until onions are soft.

Stir the brown sugar into the onions; mixture will become soggy. Reduce heat to medium-low and cook for 10-15 minutes, stirring often, until most of the moisture has evaporated and the onions appear dry.

Stir the balsamic vinegar into the onions. Reduce the heat to low and cook for 50-60 minutes, stirring occasionally, until most of the liquid has been absorbed and the onions are soft and dry.

Remove pan from heat and let onion jam cool. If desired, place onion jam in a small food processor and blitz for a few seconds until smooth.

Store jam in the refrigerator, but serve either warm or at room temperature.

Form ground beef into four roughly equal burger patties. Season patties on both sides with paprika, onion powder, salt, pepper, and parsley flakes, to taste.

Cook patties on a grill or stovetop pan until they reach desired doneness. A few minutes before removing them from the heat, place a slice of cheese on each patty. Cover with grill lid or pan lid for 1-2 minutes, allowing cheese to melt around the patty. Then remove the burgers from heat.

Arrange a few arugula leaves on the bottom half of a burger bun, then place your cheesebuger on top. Spoon onion jam on top of patty, place top half of the bun on the burger, and enjoy!