Prepare two large bowls — one for the scraps and one for the Onion (6 pound). A bench scraper is nice to have close by, too. Start by trimming off the ends of each onion, collecting scraps in one of the bowls as you go.
Next, score the outside layer of each onion.
Then use your knife to peel away the skin.
Cut each onion in half.
Slice the onions thinly making cuts perpendicular to the rings.
Place a large pot (7 to 8 quarts) over medium heat and melt the Butter (1 tablespoon). Add onions, and sprinkle generously with Kosher Salt (to taste). Cover, and cook until the onions have heated through and started to steam.
Uncover, reduce the heat to low, and cook, stirring occasionally. I cooked mine for about 3 hours at low to medium-low heat. Season with several grinds of Ground Black Pepper (to taste).
Meanwhile, preheat the oven to 200 degrees F (95 degrees C). Place the Country White Bread (6 slice) in the oven and let dry completely. You can leave the slices in the oven for a few hours, as the heat is not high enough to burn them.
When the onions have completely cooked down, the water has cooked off, and the onions have turned amber, add Water (6 cup). Raise the heat to high and bring the soup to a simmer, then reduce the heat to low.
Add the Sherry Wine (1/3 cup). Taste and season with Kosher Salt (to taste) and Ground Black Pepper (to taste) as needed. If the soup is too sweet, add the Red Wine Vinegar (1 tablespoon). If you would like a little more depth, add a splash of Red Wine (1 tablespoon).
Preheat the broiler.
Portion the soup into bowls, top with a slice of bread, cover with Gruyère Cheese (0.5 pound). Broil until cheese is melted and nicely browned. Serve immediately.