For Caramelized Onions (cook time 30 minutes)
In a small cast iron skillet, add olive oil and butter on medium heat
Once butter is melted, add sliced onions to the skillet and cover with a tight fitting lid
After about 3 minutes, remove the lid and give onions a stir
Continue this process for the next 20 minutes stirring every 5 minutes or so
Onions will begin to brown and become fragrant
At the end of cooking right when the onions begin to caramelize add kosher salt and balsamic vinegar
Give a final stir and remove the heat and set aside
To assemble skillet (prep 5 minutes, cook time 5 minutes)
In a small cast iron skillet, add 2 pieces of short ribs bone side down
To each short rib, top with a heaping of caramelized onions to taste and add shredded gruyere cheese
Broil in the oven until cheese is melted and bubbling, about 2-3 minutes (keep your eyes on it)