I've made French Onion Soup before. One of the hardest parts of making French Onion soup is caramelizing the onions. When you use your crock pot slow cooker to do all the hard work for you the onions are easy to caramelize and make the best Crock Pot French Onion Soup.
Place the first 7 ingredients into a 6 quart crock pot.
Cook on low for 8-9 hours overnight or until the onions are dark and caramelized.
Next add the beef broth and thyme to the crock pot.
Increase the temperature to high and cook for 2 hours or until simmering.
Reduce the heat to low and cook an addition 2 hours.
Add a ½ cup Parmesan cheese sprinkled over top of crock pot (or serving bowl-optional)
Before serving ladle soup into individual oven safe soup crocks.
Place a slice of toasted French bread on top of each crock, place a slice of cheese on top of the bread. Sprinkle the top of the cheese slice with the Parmesan cheese.
Melt the cheese under the broiler until golden brown.
Serve immediately.
Recipe Expert Tips
Choose the Right Onions: Yellow or white onions are typically used in French Onion Soup. They caramelize well and provide a sweet yet savory flavor that is essential for this classic dish.
Take Time to Caramelize: The key to a flavorful French onion soup is well-caramelized onions. This is a lengthy process, but it’s worth it. Cook the onions on low heat in your crockpot until they are deeply browned and sweet. Don't rush this step as it is the foundation of your soup's flavor.
Use Quality Broth: A good quality beef broth will give your soup a rich and robust flavor. If you're vegetarian, you can use a hearty vegetable broth instead. Some people also like to add a splash of dry red wine for additional depth of flavor.
Don't Skimp on the Cheese: Traditional French onion soup is topped with a slice of toasted baguette and a generous amount of Gruyère cheese. The cheese should be melted under the broiler until it's bubbly and slightly browned. This cheesy crust is one of the best parts of French onion soup, so don't skimp on it!