Preparation Melt butter in heavy large Dutch oven over medium-high heat. Add potatoes, cauliflower, carrots and onion; sauté until onion is golden brown, about 7 minutes. Add 4 cups broth; bring to boil. Reduce heat; simmer until vegetables are tender, adding more broth if soup is too thick, about 30 minutes. Season to taste with salt and pepper. (Can be prepared 1 day ahead. Cover and refrigerate. Bring to simmer before continuing.) Preheat broiler. Transfer soup to large broilerproof bowl or individual broilerproof soup bowls. Arrange bread slices atop soup. Place cheese slices over, covering bread completely. Broil 6 inches from heat source until cheese melts and is golden, watching closely to avoid burning, about 2 minutes. Serve immediately.
Preparation Melt butter in heavy large Dutch oven over medium-high heat. Add potatoes, cauliflower, carrots and onion; sauté until onion is golden brown, about 7 minutes. Add 4 cups broth; bring to boil. Reduce heat; simmer until vegetables are tender, adding more broth if soup is too thick, about 30 minutes. Season to taste with salt and pepper. (Can be prepared 1 day ahead. Cover and refrigerate. Bring to simmer before continuing.) Preheat broiler. Transfer soup to large broilerproof bowl or individual broilerproof soup bowls. Arrange bread slices atop soup. Place cheese slices over, covering bread completely. Broil 6 inches from heat source until cheese melts and is golden, watching closely to avoid burning, about 2 minutes. Serve immediately.