[Psycho Chef]

If you do it in big batches the onions need to be done in the pot so they can be stirred often because unless you have perfect pans certain areas will brown more quickly than others. Just the stirring of the onions is enough in the beginning to remove the fond from the bottom of the pan and incorporate it's flavor into the onions. However as more and more of the onions brown and loose moisture, it will lose it's ability to loosen the fond. If you are handling large batches some of the onions may not be fully cooked at this point(which will in my opinion ruin the soup). What I do then is deglaze with very small amounts of water those areas of the pan becoming too dark. Stirring this around creates a more even color and gives all the onions time to cook. Most large batches require this re-wetting technique four or five times. When about done I let one last nice frond build up the deglaze with sherry.
Ladling for service shouldn't be a problem unless you used too little onions for the amount of broth.

I am the biggest onion soup fan in the world in case you were wondering..