01 -
In a big pan, melt 2 tablespoons of butter over medium-low heat. Toss in the onions and keep cooking them on low, stirring every so often, until they soften and turn golden. This takes roughly 30 minutes.
02 -
Mix together mayonnaise, ketchup, mustard, garlic powder, and pepper in a small bowl. Once it’s blended well, set it aside.
03 -
Heat up a cast iron pan on medium-high. Melt 2 tablespoons of butter in it. Cook the patties as directed on the packaging. Clean out the pan when you’re done.
04 -
Spread your sauce on one side of all 8 bread slices. Lay out the caramelized onions on 4 of the slices. Add a burger patty on top of each, followed by a slice of cheddar and a slice of Swiss. Place the leftover bread slices on top to close them.
05 -
Melt 2 tablespoons of butter in a pan on medium-low. Gently place the sandwiches in the pan and cook until one side is golden brown. Flip them, add 2 more tablespoons of butter, and carefully move the sandwiches around to soak up the butter. When both sides are golden, they’re ready to eat.