Elegant French Onion Soup with Sourdough Crust

Ingredients:
3 tablespoons unsalted butter, chunked
6 large yellow onions
1 teaspoon sea salt and ¼ teaspoon sea salt
½ cup dry Sherry
4 cups high quality low-sodium chicken broth
2 cups high quality beef broth
6 sprigs fresh thyme, bundled and tied with kitchen string
1 bay leaf
ground black pepper, to taste
1 sourdough baguette, cut into ½ inch slices
8 oz shredded Gruyere cheese
Directions:

Place oven rack to the bottom center position.
Preheat oven to 400 degrees.
Generously coat the inside of a heavy-bottomed large Dutch oven with non-stick cooking spray.
Peel onions and cut them in half. Then, put pieces sliced side down and cut ¼ inch wedges by cutting across the center like a pizza.
Put butter, then onions and salt in the pot.
Cover and bake in preheated oven for one hour.
Remove from oven and stir, scraping the bottom and sides of pot.
Position the lid off-center on the pot and return it to the oven to cook until the onions are golden brown (about 1 ½ hours).
After about 1 hour of cooking, stir and scrape bottom and sides of pot, then return it to the oven for the last ½ hour.
Remove pot from oven and place it on range burner over medium-high heat.
Cook for 15-20 minutes until liquid is evaporated and onions are browned, scraping sides and bottom of pot frequently.
Reduce heat to medium and continue to cook and scrape for 6-8 minutes until bottom of pot is completely covered in a dark crust.
Stir in ¼ cup water and continue to cook and scrape (dark crust should release into water as you scrape).
Continue until another layer of crust has developed on the bottom of the pan and the liquid is evaporated.
Repeat the deglazing process two or three more times until the dark layer is thick and onions are a dark brown.
Repeat the step one more time, but with the Sherry instead of water.
Add broths, 2 cups of water, thyme, bay leaf and ½ teaspoon salt to pot, scraping any remaining bits of crust from bottom and sides of pot.
Bring soup to a boil over high heat, then reduce heat to low, cover and simmer for 30 minutes.
Meanwhile, prepare the sourdough croutons by first arranging the slices on a baking sheet in a single layer.
Return oven rack to center position.
Toast bread in the 400 degree oven for about 10 minutes or until the edges are golden brown and the center is very dry.
Reposition the oven rack again, six inches from top element broiler.
Soup should be done simmering by now, so turn heat off, remove herbs and season with salt and pepper to taste.
Fill individual oven/broiler safe crocks (the ones with handles make it much easier) with soup.
Gently place two slices of toast on top of soup. Sprinkle toast with Gruyere cheese.
Broil for 3-5 minutes or until cheese is melted and the edges are bubbled.
Remove from oven to cool five minutes before serving.