French Onion Soup

I love French Onion Soup. It's one of my favorite things to eat. I especially love dipping bread in it. Super yum! I first started making this soup last winter, and I've been so anxious for the weather to finally cool off so I could make this soup and share it with you all. Trust me, this is a soup you need to make. It's awesome. Not only that, but it's easy - well, outside of the face that cutting the onions will totally make you cry. This is a perfect recipe for fall and winter, and oh so tasty.

French Onion Soup
adapted from The America's Test Kitchen Family Cookbook

2 tbsp unsalted butter
5 medium red onions (about 3 pounds), halved and sliced thin
2 tsp minced fresh thyme or 1/2 tsp dried
Salt
1/4 cup balsamic vinegar
6 cups low-sodium chicken broth
1 3/4 cups low-sodium beef broth
2 bay leaves
Pepper
Baguette, sliced 1/2" thick
8 oz Swiss cheese, shredded (2 cups)

1. Melt the butter in a large Dutch oven over medium heat. Add the onions, thyme, and 1/2 tsp salt. cook, stirring occasionally, until the onions are dark and sticky, about 30 minutes.
2. Stir in the vinegar and scrape the browned crust from the pot. Stir in the chicken broth, beef broth and bay leaves. Bring to a simmer and cook for 20 minutes. Season with salt and pepper to taste and discard the bay leaves.
3. Adjust an oven rack to the middle position and heat the oven to 450 degrees. Arrange oven-sade soup bowls on a rimmed baking sheet and ladle the soup into them. Top each bowl with 2 baguette slices and sprinkle each with 1/4 cup cheese. Bake