Easiest French Onion Soup

From the book Not Your Mother's Slow Cooker Cookbook.

• Ready In: 10 hrs 40 mins
• Serves: 4-6

Ingredients

• 6  large yellow onions
• 3  tablespoons olive oil, plus extra
•  olive oil, for brushing
• 1 (14 ounce) can chicken broth
• 1 (10 1/2ounce) can beef broth
• 2  tablespoons marsala (optional) or 2  tablespoons red wine (optional)
• 4 -6  slices  French bread
• 8  ounces gruyere cheese, cut into slices

Directions

1. Peel and thinly slice the onions by hand or in a food processor. Put in the slow cooker and toss with olive oil. Cover and cook for 9 to 10 hours on High.
2. Add both the broths and Marsala, if using; add no water or salt. Cover and continue to cook on High until hot, 15 to 30 minutes.
3. Meanwhile, preheat the oven to 400 degrees F. Put the bread slices on a baking sheet and brush with olive oil or leave plain. Bake until golden brown around the edges, about 10 minutes. Set aside.
4. Ladle the soup into individual ovenproof soup bowls and place on a baking sheet. Top each bowl full of soup with a toasted bread slice and cover with a slice of the Gruyere. Adjust the oven rack to comfortably fit the bowls under the broiler with at least 4 inches to spare. Turn on the broiler and slide the soups under the flame; broil until the cheese is melted and bubbly, 1 to 2 minutes.