Step 1: Onions
For this recipe I've used 6 large onions, halved and sliced. Modify the number to suit your preferences.
Add the onions to a large heavy pot greased with a couple of tablespoons olive oil, butter, canola oil, or some combination thereof. I find adding even a little bit of butter goes a long way in improving taste.
Add a couple of bay leaves and some black pepper, and stir over medium heat.
Add a handful of chopped garlic when the onions have begun to soften.
The goal is to slowly brown the onions to create a nice strong caramelized flavor for the soup. Stir more frequently as they cook to prevent sticking.
Step 2: Deglaze with sherry
Add approximately 1/2c sherry and stir, scraping the bottom to remove all the tasty bits as the sherry cooks down.