Every recipe tells you to slowly cook onions for more than an hour to get them jammy, sweet, and deeply caramelized. Low and slow, stirring almost the whole time, waiting for that deep brown color to build. It works, but it eats most of an afternoon.
But with a little science, we can make it much faster. The slow part of caramelizing is breaking the onions down, and a microwave does that fast because it targets the water inside the cells and bursts them open. Ten minutes in the microwave gets you the structural breakdown that an hour of slow stovetop cooking is really after. From there it all goes into the pan, liquid and all, and cooks down on high heat. Every splash of water you add breaks the fibers down further and keeps the bottom from burning, until the onions melt into soft, jammy strands. A spoonful of brown sugar leans into the onion's heavy natural sweetness, a knob of butter makes everything rich and glossy, and a pinch of salt at the end is all it needs.