4-6 Tablespoons unsalted cold butter, divided
12 yellow onions. Peeled and sliced in 1/4 inch rings
1 Tablespoons good quality olive oil
1 teaspoon kosher salt
1/2 -1 teaspoon fresh ground pepper
6-8 cups the best quality, low-sodium beef broth
1 large bay leave
4 sprigs of fresh thyme
4 sprigs of fresh flat leaf parsley, bundled
1 large fresh baked loaf of French bread
4 garlic cloves- cleaned. 2 minced very fine / 2 cut in half-lengthwise
4-6 teaspoons good quality Sherry
4-6 ounces Gruyère cheese
In a large Dutch oven, or 6-8 quart stock pot-melt 4 Tablespoons of the butter over medium heat with the olive oil. Add the onions.
Sauté onions until they are soften stirring occasionally, about 15 minutes.
Add the salt, black pepper and finely minced garlic. Continue to cook, stirring occasionally-until onions are turning a deep brown and beginning to caramelize. ( Reduce heat slightly if onions seem to be browning too quickly – onions contain a large amount of sugar– and sugar can quickly burn over high heat.)
Cook an additional 20 minutes until all onions are a deep rich chocolate brown.
Add one cup of stock to the pot and quickly deglaze the bottom of the pan by stirring and scraping, making sure to release all the delicious flavors that are stuck on the bottom. Add the remaining beef stock.
Tie the thyme, bay leave and fresh parsley into a bundle with twine. Add the herb bundle to the pot.
Bring to a boil, then immediately reduce to a simmer. Cook uncovered, until broth is reduced, thickened and flavorful- about 20 minutes.
Remove from heat and whisk in remaining 2 tablespoons cold butter. Taste and adjust seasoning with salt and pepper.
Heat the broiler. Cut a 1/2-inch slice of French bread for every serving of soup.
Place bread slices on a rimmed and lined baking sheet- toast bread slices in the oven until crisp, but not too brown. About 1 -2 minutes per side.
Remove from the oven and generously rub one side of each piece of toasted bread with a fresh raw cut garlic clove. Set aside.
Place oven safe bowls, or large soufflé ramekins on the rimmed baking sheet, add 1/2 teaspoon of sherry to the bottom of each, and ladle soup on top. Top each serving of soup with garlic-rubbed toast. Divide cheese among the bowls, covering the bread and some of the soup.
Carefully transfer baking sheet to oven and broil until cheese is melted and bubbling, 5 to 8 minutes.