For the caramelized onions
- 2 tablespoons butter
- 3 pounds yellow onions (5 medium)
- 1 teaspoon kosher salt
- 1/2 cup dry sherry (or white wine)
- 1 tablespoon flour
For the soup
- 2 tablespoons butter
- 8 ounces mushrooms
- 1 carrot
- 2 celery ribs
- 6 garlic cloves
- 9 cups water, divided
- 2 tablespoons tomato paste
- 1 teaspoon each garlic powder and onion powder
- 1 teaspoon vegan Worcestershire sauce (purchased or use this substitute)
- 2 teaspoons kosher salt
- 6 slices Swiss or Gruyere cheese (or shredded)
- 6 tablespoons grated Parmesan cheese
- 6 large or 12 small slices bread, sliced about 1/2” thick