Ingredients
- 3 pounds yellow onions, peeled, cut in half and sliced, thin
- 2 tbsp. unsalted butter, melted
- 2 tbsp. olive oil
- 2 1/2 tsp kosher salt
- 1/2 tsp freshly ground black pepper or more as you like
- 2 sprigs fresh thyme
- 1/4 cup balsamic vinegar
- 8 cups beef broth
- 1/3 cup brandy, highly recommended but optional
- 4 to 6 baguette slices, toasted
- 1 1/3 to 2 cups grated Gruyere cheese
Preparation
Step 1
First, place all your onions in a 5-quart or larger slow cooker. Then drop in your melted butter, olive oil, salt, and black pepper. Give it a nice stirring up.
Then cover your crockpot and cook it on low for 10-12 hours. If you’re making this soup for an event, you can cook if overnight if you’d like. When the onions become soft and turn a dark golden brown, you’re ready to move onto the next step.
Pour the wet ingredients into the pot, including the beef broth, balsamic vinegar, and then the fresh thyme.
Cover and cook again for an additional 6 to 8 hours on low.
When that’s done, season with more salt and pepper to taste. And if you want, which is highly recommended for a fuller flavor, add the brand.
Then preheat your oven to 350°F. Ladle the soup into oven-safe bowls. Place these on a baking sheet.
Top each bowl off with the sliced baguette pieces and then cover with shredded Gruyere cheese. Bake them for 20 to 30 minutes. And you’ll know when it’s done because the cheese will have completely melted.
Then turn the oven to a broil and brown the tops of your bowls for 2 to 3 minutes. You can add a little more cheese before this step.
When that’s done, you’re ready to serve. Just make sure they’ve cooled a bit before someone burns their tongue.