If you're just starting out cooking or eating onions, stick with basic yellow onions. We find these to be the all-around best for just about any dish we cook and at whatever intensity we want them. Other kinds of onions have different flavors or characteristics that make them ideal for specific dishes, though they can all be cooked in the same ways.
• Raw - If you leave onions uncooked, their flavor will be sharp and pungent, and their texture will be crisp and crunchy. Raw red onions are especially good in salads. You can remove some of their astringent flavor by soaking them in cold water before adding them to the dish.
• Quick Cooking Over High Heat - A minute or two over high heat is just enough time to take the edge off the oniony flavor, but leaves the texture nicely crisp. This is exactly what you want in Asian stir-fries or when grilling onions for shish-kabobs. Don't leave the onions on high heat for too long or they will soon start to burn.
• Slow Cooking Over Medium Heat - Pour a teaspoon or so of oil in the pan and add the onions along with a pinch of salt. Stir them every few minutes until the edges of the onions start to soften and the middles turn translucent, about ten minutes. At this point, the pungent onion flavor is gone, leaving behind a mild sweetness. If you continue cooking until the onions start to turn brown, you'll notice nutty and caramel flavors starting to emerge.
This is the technique we use the majority of the time when cooking onions. It's perfect for the start of soups, sauces, pilafs, frittatas, and just about every other savory dish we cook. Once cooked, the onions no longer have such an upfront in-your-face flavor. They blend into the background and create a base for the rest of the flavors in the dish.
• Slow Cooking Over Low Heat (Caramelizing) - If you turn the heat down to low while you cook your onions, their flavor and texture transforms even further. They will gradually brown, become completely limp, and even start to disintegrate. They caramelize and taste sweeter the longer you cook them - even up to an hour or more. Caramelized onions can be used to make French Onion Soup, to top pizzas, in salads, or as a side dish all their own. Read about the full technique in this post on how to caramelize onions.
Do have a favorite way of cooking onions?