Peel the onion(s) and cut off the ends. Slice them thinly into even rings or strips.
In a medium-sized, heavy-bottomed pot, heat the butter over medium-low heat. Allow the butter to melt completely.
Begin by adding half of the sliced onions to the pot. Stir to coat them evenly with the butter and oil. Sprinkle with a pinch of salt if desired (you will adjust the seasoning later). Slowly add the remaining half of the onions. (You may need to cook in batches depending on your pan size and amount of onions, do not overcrowd the pot.)
Cook the onions over medium-low heat in the pot, stirring occasionally. It’s crucial to cook them slowly to caramelize properly. The onions will go through several stages: first, they will become soft and translucent, then they will gradually turn golden brown.
Caramelizing onions takes time. Depending on your desired level of caramelization, it can take anywhere from 30 to 40 minutes. Stirring every few minutes helps ensure even cooking.
If the onions start to brown too quickly, reduce the heat to prevent burning. If they’re not browning at all, increase the heat slightly.
Taste the onions as they cook. Once they’ve caramelized to your liking and have a sweet, rich flavor, you can add more salt to taste. If desired, you can also add a pinch of pepper for extra flavor.
Once the onions have reached your desired caramelization, remove them from the pot. They are now ready to use as a topping for burgers, sandwiches, steaks, or as a addition to various dishes like soups and stews.
Notes
The caramelization process requires patience. Avoid the temptation to increase the heat to speed up the process, as this can lead to burning rather than true caramelization.
If you prefer, olive oil or a mix of butter and oil can be used for a different flavor profile or for dietary preferences.
If your pot isn’t large enough to hold all the sliced onions without crowding, consider cooking them in batches to ensure even caramelization.
Caramelized onions can be stored in an airtight container in the refrigerator for up to a week. They can also be frozen; simply thaw and reheat before using.
Caramelized onions add a rich, savory flavor to a variety of dishes like burgers and steaks. Get creative and try them on grilled cheese sandwiches, pizzas, or mixed into mashed potatoes for an extra layer of flavor.