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  1. To a medium pot, set over medium-low heat, add the olive oil, butter, onions and a few pinches of salt.
  2. Cook until softened, about 5 minutes.
  3. Spread the onions out into an even layer on the bottom of the pan. Stirring occasionally, cook for about 10 to 15 minutes until caramelized.
  4. Turn the heat to medium-low and cook for an additional 15 minutes, again, stirring occasionally.
  5. Add the mushrooms and continue cooking until the mushrooms are softened, about 10 minutes.
  6. Add the water and bring to a gentle simmer. Cook for about 5 to 7 minutes.
  7. Give it a taste and adjust the salt to your liking.
  8. Divide the soup amongst the soup bowls. Top with slice of bread and a huge handful of shredded cheese.
  9. Transfer to a baking sheet and place it under a broiler until the cheese is melted and bubbly, about 5 minutes. Serve immediately.
  • 1 tablespoon olive oil
  • 1 tablespoon unsalted butter
  • 2 yellow onion, peeled and thinly sliced
  • Salt to taste
  • 8 ounces cremini mushrooms, thinly sliced
  • 5 cups of water
  • 6 ounces Gruyere cheese, grated
  • French bread, sliced