2 slices cheese that melts well, like provolone or cheddar
2 burger buns, lightly toasted
Heat the olive oil in a skillet on medium high. Stir in the onions with a pinch of salt. Cook on medium high for 5 to 10 minutes, stirring infrequently so that the onions will brown.
When the onions have begun to brown nicely, add the butter to the skillet and lower heat to medium low. Cook for another 10 minutes until the onions are very soft and brown. Keep on low heat until the the burger is ready.
Make the guacamole as the onion caramelizes. Slice the avocados in half. Remove the pit, then scoop the flesh into a bowl.
Mash the avocado with a fork, then stir it a bit. Stir in the garlic.
Add the add the cilantro, salt and pepper. Stir again.
Add the lime juice. Stir vigorously to get everything well combined and to achieve a nice fairly smooth consistency. Set aside.
As the onion continues to caramelize, cook the burger. Heat a skillet on medium high with oil spray. When the skillet is good and hot, add the burger to the skillet. Sprinkle with a pinch of salt. Lower heat to medium.
Cook burger 5 to 6 minutes on one side, then flip to cook another 5 to 6 minutes. Add the cheese, cook another minute or two until the cheese has melted. It is recommended to serve ground beef medium to medium well done.
Place the cooked burger onto a bun. Top with some guac, and spread to cover the burger. Top with the caramelized onions, and enjoy with a glass of Cab Franc!