Techniques
How do you caramelize onions?
The short answer. Cook thinly sliced onions in butter or oil over medium-low heat, stirring often, for 20 to 25 minutes or longer, until they are deep golden and sweet.
Patience is the technique. Low heat lets the natural sugars in the onion brown slowly without burning, and the onion softens into a jammy texture.
Add a pinch of salt at the start to draw out moisture. If the pan looks dry or the onions start to stick, add a splash of water and keep going.
Where it shows up in our recipes
Question
Why are my onions bitter?
The heat was too high and they burned instead of browning slowly. Lower the heat and stir more often.