French Onion Soup

Heat oil and butter in a large Dutch oven over medium-high heat. Stir in yellow onions and sweet onions; cook, stirring occasionally, until softened, about 5 minutes. Decrease heat to medium-low; cook, stirring occasionally, until the onions are golden brown, about 30 minutes. Continue to cook, stirring often, for 10 minutes. Stir in 1 tablespoon water; scrape the brown bits from the bottom of the pot with a wooden spoon. Continue to cook, stirring often, until the onions deepen in color, about 10 minutes more.

Stir in wine and vermouth, scraping the brown bits from the bottom of the pot. Cook, stirring often, until the liquid has evaporated, about 5 minutes. Stir in flour until the onions are coated, about 1 minute. Stir in broth, thyme, garlic, pepper, salt and bay leaf; bring to a boil over high heat. Reduce heat to medium-low; simmer until slightly reduced and thickened, about 20 minutes.

Meanwhile, preheat oven to 400°F. Place 6 ovenproof bowls on a rimmed baking sheet.

Stir chives and parsley into the soup; remove and discard bay leaf. Divide the soup among the prepared bowls. Place 1 toast slice on top of each bowl; sprinkle each with 2 1/2 tablespoons cheese. Bake until the cheese melts and is slightly browned, about 5 minutes. Garnish with additional chives and parsley, if desired.