To do a modest amount of caramelized onions that can be done in a single pan, I prefer doing them in an enameled pan as it gives a better modulation of the heat. I start them off with a lid to soften them up, then remove it so that they will caramelize. When doing larger amounts I have to go to other larger pans and find my old thick restaurant grade aluminum pans work much better than ss (including All Clad & Cuisinart, which both tend to burn if not watched continuously). (What I hoped in my original query was to draw on the experience of others who may have used the oven to find out if it can be done in large quantity without standing over it. I find it hard to believe that restaurants do it the same laborious ways I have been doing.)
Seasoning will vary according to my intended use. If I use them for a pissaladiere, I add only a pinch of salt as I want the contrast between the sweetness of the onions and the saltiness of the anchovies and olives. For other uses I might salt them more. I find most onions are sweet enough without adding sugar, but tasting them along the way will determine that. I usually use either Spanish, Red, or sometimes Vidalia. In fact, my more usual addition is a touch of either Spanish, Banyuls, or Rice (I've seen recipes calling for Balsamic, but I prefer these) vinegar or some Port or other wines to make the flavor a little more complex. Sometimes I will use a little thyme or other herbal flavors either during cooking or when I assemble the dish. Obviously, seasonings are totally flexible depending on final use.
