In making my own base and stocks, it all starts with onions. It seems cooks are always chopping and browning onions. Julia Child famously practiced simply chopping onions when she attended cooking school in Paris. Many recipes start with browning onions. Browning the onions combines their proteins and sugars. The taste is quite different from steamed or boiled onions. Browning onions usually takes longer than the recipe claims. Browning onions happens in stages: translucent, golden and finally brown. It's unnecessary and counterproductive to use any fats or oils, or even a non-stick pan. (You want the onions to stick slightly.) Too much heat, and the onions blacken and burn.
1 onion, chopped
Soften: Place onions in regular (not non-stick) saucepan, over medium heat, with lid on. Allow the onions to steam, until they become translucent, 5-10 min. The moisture in the onions becomes steam, and largely keeps the onions from burning. During this time they can mostly be ignored, except perhaps for an occasional stir. You usually catch an aroma when they're done.
Taste test the plain translucent onions.
Brown: Remove the lid, and continue to cook, and allow onions to almost burn slightly, another 5-10 min. As the onions loose moisture they will begin to turn golden and stick to the bottom of the pan. Stir with a wooden spoon, scraping the bottom of the pan. If necessary, use a bit of cold water to deglaze the bottom of the pan, scraping the loose bits from the bottom with a wooden spoon. I usually stop here, when onions are nice golden brown.
Taste test the golden onions.
This process goes faster if you use high heat, watch closely, and stir and deglaze often. This results in fully brown onions. Taste test the brown onions.
Brown onions in advance, and store covered 2-3 days in refrigerator.
Cook uncovered during softening to speed the process. But watch more carefuly.