The first thing we choose how we want the caramelized onion to be. I usually prefer it to be in long strands, so to achieve that short effect the onions in julienne, but if you prefer it to be like jam, in that case you should cut the onions in brunoise. As we are going to chop a kilo of onions, remember the tricks so as not to cry with that operation.
We put a wide frying pan with olive oil and add all the onion, adding a handful of salt and stir well so that all the strands are slightly impregnated with oil. With the heat set to low, the onion will take approximately 5 minutes to start poaching.
To speed up the process and to caramelize the onion in about half an hour, we add a dessert teaspoon baking soda sprinkling it over the onion. With the bicarbonate, the natural sugars in the onion and part of its water come out earlier. After a couple of minutes, the onion is yellowish in color and appears to be swimming in liquid.
We continue to reduce the onion slowly, stirring from time to time until the onion darkens as its sugars turn into caramel and while the water evaporates. After 30 minutes the onion is perfectly caramelized and ready to use. Of course, the kilo of onions has reduced so much in size that we will barely fill half a jar of jam.
How to intensify the caramelization?
Even though I I prefer to use the caramelized onion in its own sugars, the process can be finished by giving a more sweet touch and a more intense color by adding the optional ingredients when the onion has already been caramelised, after 30 minutes.
In that case, we add two tablespoons of sugar (white or brown) and stir for two or three more minutes until the sugar has disappeared, transforming into more caramel and darkening the onion. You can also add a splash of Aceto of Modena or its reduction, obtaining interesting acid notes that contrast with the caramelised onion.