cook, stirring every 45 minutes, until the onions are
completely tender, about 2 hours.
Remove the lid and increase the heat to medium-high.
Cook, stirring frequently, until the liquid has evaporated
and a brown patina has started to form on the bottom of
the pot, about 15 minutes. Add 2 tablespoons water and
scrape the browned coating from the bottom of the pot.
Shake the pot to distribute the onions evenly over the
bottom and cook, shaking occasionally, until the liquid
evaporates and the browned coating starts to build up
again, about 5 minutes longer. Add 2 more tablespoons
water and repeat, allowing the coating to build up and
scraping it off, then repeat two more times. By this point,
the onions should be a deep brown. If not, continue the
deglazing and stirring process until the desired color is
reached.
- Add the sherry, chicken stock, bay leaves, and thyme,
bring to a boil, and reduce to a simmer. Simmer,
uncovered, until the liquid is deeply flavored and slightly
reduced, about 15 minutes. Season to taste with salt and
pepper. Discard the bay leaves and thyme. - To serve, heat the broiler. Ladle the soup into four
broilerproof bowls. Float the croutons on top and cover
with the grated cheese. Broil until the cheese is melted,
bubbly, and golden brown in spots. Serve immediately.