Any type of bulb onion can be used, as they all have sugar, but white or yellow onions look prettier. Red onions will have the flavor, but not be as visually appealing with a funky color. I tend to use a sweet onion, purely because that is what I have always used, but it is not necessary.
A Couple of things to keep in mind:
- Cut onions into as uniform of slices as you can. Thicker onions take longer to cook, thinner less time to cook. Ideally you would like your onions to all caramelize at the same pace.
- This is a slow process. Trying to speed it up with produce sauteed onions, but they will lack the sweet taste you are trying to achieve. Be patient.
- Use a large frying pan, preferably with a heavy bottom. This provides the largest amount of cooking surface and allows you to better control the temperature.
- Don’t over stir. Stirring too much will result in mushy onions. Use more of a tossing maneuver to rotate onions. You will need to toss more towards the end of cooking.
- I add a teaspoon of sugar to my onions, but many do not. Your choice, you can leave it out using only the sugar naturally produced by your onions.
- Depending on your pan, you may have some sticky, brownish bits stuck to the bottom of your pan. No worries, you didn’t burn your onions. Just de-glaze with a splash of white wine and scrape them up.
- Caramelized onions freeze well and can be kept in the refrigerator for up to 4 days.
- Caramelized onions also freeze well in airtight plastic bags.