Prepare the onions by removing the skin and the stem and root of the onion. Cut the onion in half from top to bottom. Make angled cuts into the onion along the natural lines that appear on the onions. Separate the slices and set them aside. Continue through all four or more onions.
Add the butter and sliced onions to a large stainless steel pan or cast iron pan over medium heat. Stir so that the onions are coated with the butter and sprinkle the salt evenly over the top.
Lower the heat to medium-low and continue to stir the onions every one to two minutes, allowing them to caramelize on the bottom of the pan in between stirring for 40 to 45 minutes or until caramelized to your liking. If your onions are sticking or if the bottom of the pan starts browning too much, add a splash of water (no more than 2 tablespoons) to deglaze the pan and add color to your onions.
Use immediately or allow to cool before storing in the fridge.
Notes
The key to success here is to cook low and slow - don't try to rush it!
If you use salted butter, be sure to consider that when seasoning with any additional salt.
Do not cover the pan while cooking.
How to store Caramelized Onions?
Store them in the fridge for up to 5-7 days.
Can you freeze Caramelized Onions?
Yes! Allow them to cool completely before transferring them to a freezer-safe container or zip-top bag. Freeze for up to 3 months. Thaw them in the fridge when you're ready to use them. TIP: I like to freeze small amounts in an ice cube tray and then transfer the cubes to a large zip-top bag so I can add the cubes to recipes as needed!