From the comments: A relatively fast method which involves baking soda, sugar, and water. However, it still takes longer than the 4 or 5 minutes reported in many recipes.
Quoted in full from the comments because they don't seem to have permalinks:
If someone browns onions for a majority of their dishes, it is Indians! Let me tell you one thing: if you take 45 minutes to brown onion, you would not be able to get an Indian meal ever cooked on time Smile
So, how long does it take to brown onions? First, it depends on the quantity. A small onion here (which would be about a medium to medium-large onion in India) should not take more than 15 minutes. So, why does Madhur Jaffery, who you have referred to in the article, still say 5 minutes? That brings us to the second factor: onions in India are much drier (i.e., they have a much lower water content than we have here). In fact, people in India seek out drier onions in a market because it takes significantly less time to brown them! In addition, drier onions have matured enough, so they are better for cooking. Here, in the US, the water content in the onions, and practically every vegetable, is much higher. So when one tries to brown onions, significant time is spent first evaporating the water, thus adding to the time it should actually take to brown them!
A third reason is experience (or lack thereof). Experienced cooks will brown onions much quicker than amateurs, or people who do not cook as much, would.
Butter will brown onions faster not because the water in them has evaporated, but because butter tends to brown easily. That does not cook the onion completely, something that would not be suitable for Indian curries.
Ever since I came to this country (almost 27 years now), I have cooked meals. For me, spending 45 minutes on browning onions would be blasphemy . . . I have kids and other work to attend to and they would miss school the next day because dinner was so late the previous evening. Personally, I can brown a small onion here (without burning it on high heat!) in about 10 - 12 minutes. For me, 20 minutes browning a small onion would be too long, even if I do other stuff (such as chop veggies).
Hope this explains why we think that chefs must not be telling the truth about browning onions.
ETA Turning onions into flavor bombs Long slow cooking, and a little of the science. It's mentioned that carmelizing involves breaking down the cell walls in the onion. I wonder whether hammering on the onion first would help. Experimentation is required.
Link thanks to andrewducker.
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