In doing some bulk cooking for a vacation, I needed to cook 12 sliced onions and later 6 minced onions for two different dishes; both as a first step in a sauce. In both cases, I used a large Le Creuset dutch oven. I found that the evaporation of the liquids shed from the onions couldn't keep up with the volume of liquids and I seemed to be boiling the onions rather than sauteing.
For the sliced onions, I ended up removing half the volume, draining off the liquid, cooking the onions, and boiling down the liquid to add back to the sauce at a later step. The onions boiled / simmered for 30 mins before I took that action. The dish was fine, but was a curry, so had lots of other flavor. It was also distinctly better after I added the boiled down liquid.
With the minced onion, the liquid eventually boiled off and I continued to cook them. It felt like it took a long time to get to that stage though. The dish was fine, but the texture of the onions was different than how I normally prepare them.
Are there appropriate steps to take when cooking mass quantities of onions as a first step in a dish? Is it ok for them to go through the boil / simmer phase? Should they be cooked in batches? What recipe adjustments should be made?