01 -
On low heat, stir onions every now and then for 30-35 minutes with butter after cooking 5 minutes on medium with a lid on. Add vinegar at the end to scrape up the browned bits.
02 -
Shape 3 burger patties. Season them right before cooking, then heat your cooking surface to between 375-400°F.
03 -
Heat oil, cook each side of the patty for around 3 minutes.
04 -
Spread butter on both sides of the bread, then toast them on your hot griddle for 1-2 minutes per side.
05 -
Stack your toasted bread with a burger patty, cheese, and those caramelized onions on top. Press the sandwich together and enjoy.