- 2 portobello mushroom caps, cubed
- 2 tablespoons all-purpose flour
- 1 tablespoon olive oil
- 2 potatoes, cubed
- 2 carrots, sliced
- 1 onion, sliced
- 3 cloves garlic, minced
- 4 sprigs fresh rosemary
- 20 fluid ounces stout beer
- 1 1/2 cups vegetable broth
- 1/2 (6 ounce) can tomato paste
- 2 teaspoons Worcestershire sauce
- 1 teaspoon salt
- 1 teaspoon ground black pepper
- 1 1/2 teaspoons cold water
- 1 1/2 teaspoons cornstarch
- 4 slices French bread
- 1/2 cup shredded Swiss cheese
- Toss mushrooms and flour together in a bowl until coated.
- Heat olive oil in a large skillet over medium heat; cook and stir coated mushrooms until browned, 5 to 10 minutes.
- Combine potatoes, carrots, onion, garlic, and rosemary in a large stockpot; top with cooked mushrooms. Stir beer, vegetable broth, tomato paste, Worcestershire sauce, salt, and pepper into vegetable mixture. Cover stockpot and cook over medium-high heat until vegetables are tender and soup flavors have blended, about 1 hour.
- Whisk water and cornstarch together in a bowl until dissolved; stir into soup until thickened, about 3 minutes.
- Set oven rack about 5 inches from the heat source and preheat the oven's broiler.
- Arrange bread slices on a baking sheet and sprinkle Swiss cheese over each slice.
- Broil bread in the preheated oven until cheese is melted and golden, about 1 minute.
- Ladle soup into bowls using a slotted ladle; top each with a bread slice. Ladle broth over bread until saturated.
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