How to Properly Caramelize Onions
True caramelization is about managing time and moisture. You are not just softening onions; you are breaking down their cellular structure and encouraging a slow chemical reaction that changes the color and depth of the vegetable entirely.
Patience is your primary ingredient.
Do not attempt this if you are in a rush. If you turn the heat up to make them brown faster, you will lose the sugar development and only end up with bitter, scorched onion bits.
- Heavy-bottomed stainless steel or cast iron skillet
- Wooden spatula
- Sharp chef's knife
What goes in.
- 3 largeyellow onions, halved and sliced pole-to-pole
- 2 tbspunsalted butter
- 1 tbspneutral oil
- 1/2 tspkosher salt
Recovering the fond
When a brown film develops on the bottom of the pan, add a splash of water or stock. Scrape the pan with your spatula to lift this sticky residue; it contains the essence of the onion.
The method.
Heat the fat
Place the skillet over medium heat and add the butter and oil. Once the butter is melted and foaming, add the onions.
Initial sweat
Toss the onions to coat them thoroughly. Cook for about 10 minutes until they soften and become translucent.
Slow cook
Reduce the heat to low. Add the salt, which helps draw out moisture. Stir every 10 minutes, being careful to scrape the bottom of the pan.
Deepen color
Continue for 45 to 60 minutes. As the onions turn from pale gold to a deep, dark brown, you will need to stir more frequently to prevent burning.
Finish
The onions are finished when they are uniform in color and have reduced to roughly one-quarter of their original volume.
Other turns to take.
Balsamic Finish
Add a teaspoon of balsamic vinegar in the final minute of cooking to brighten the deep sweetness.
Thyme Infused
Toss in two sprigs of fresh thyme midway through the cooking process.
When it doesn't go to plan.
Slice the onions pole-to-pole (root to stem) rather than into rings; they hold their shape better during the long cooking process.
If the onions look dry but aren't brown enough, add water a tablespoon at a time.
Caramelized onions freeze well, so consider cooking a double batch.
The ones that keep coming up.
Can I use a non-stick pan?
You can, but you won't get the same build-up of brown bits (fond) on the bottom, which contributes to the final depth of flavor.
How do I know they are burned?
If they taste acrid or bitter, or if they turn black rather than deep brown, they have moved past the point of caramelization.