Gently softening onions in a small amount of fat is the very first cooking step in many soup, stew, sauce, vegetable, grain and legume recipes. There’s probably no reason for me to say it is an important step in making most of your recipes. The process is called sweating, and there are generally two ways to go about this: gently softening vegetables or completely caramelizing their sugars.
Sweating onions and vegetables is simple to do without using oil, which is perfect if you are looking to cut back or eliminate the use of fats and oils. Here are my suggestions. You will want to use option number 2 to create a very intense and dark puree.
Option 1 (this is for soups, sauces and stews)
Heat a heavy bottomed pot or pan over medium heat. Add the onions to the pan. You should hear a sizzle at this point and that is good because it means your pot or pan is hot enough. Now, add a small pinch of salt to the onions (I use 1/2 teaspoon per onion) and stir well. The salt will penetrate the onions and they will release their water, which is good. Keep cooking the onions over medium-low heat until all the water has evaporated and the onions turn translucent. Make sure to add a bit of water if the onions begin to stick too much and take on color. You are just looking to soften the onions at this stage and remove their raw flavor rather than caramelizing them and adding sweetness.
Option 2 (this is to create color, say for a brown sauce)
Heat a large stainless steel pan over medium heat. The pan has reached the correct temperature when a few drops of water immediately swirl in the pan like mercury balls. At this point, add the chopped onions and immediately season them with salt to help release their water. Allow the onions to gently stew in their juices until they begin to stick on the pan. Release the onions and their juices by adding 1-2 tablespoons of water and gently scraping the pan with a spatula. Continue with the same process until the onions reach a nice golden color and their juices become brown. This will take 10-15 minutes, so be patient.Go back to techniques