In some places they will serve raw onion on a burger, others make an onion Smashburger (see technique further on) most of the time a burger will have caramelised onion.
Nothing will make you as hungry as the smell of onions frying!
One of the big Burger Chains in the US puts the onions on the grill first and smashed the burger patty on top of them so they are pressed into the meat!
The brown look and the caramel flavour come from the sugars in the onion being released in the cooking and forming a caramel in the pan. I add a little sugar and some salt to extract the moisture and to promote the browning.
5 large onions will make 2 cups of Caramelised onion.
I pre make mine ahead of time and just warm them on the grill for service.
Caramelising onions can take an hour
4-5 medium or large onions, brown, white, or red
Extra virgin olive oil
Balsamic vinegar, optional
Oregano, Rosemary, Sage, or Thyme (Optional)
Peel and slice the onions.
Heat a tablespoon of oil (and the same amount of butter if using) in a skillet or saucepan over a medium heat.
Add the onions and stir to coat with the oil.
After 10 minutes add a pinch of salt and/or sugar to the onions, limit the salt but you can add a teaspoon of sugar or more to help with the caramelisation. Add the herb at this poing iof you are doing that.
Leave the onions sit for a bit so they start to brown on the bottom of the pan, stir only occasionally until they are a lovely golden brown colour, this can take an hour or so.
If the onions start to dry out add a spoon of water or two, if using balsamic, add that.
Once the onions are caramelised, store them in a bowl in the fridge till you need them.