Slow Cooker French Onion Soup

I know it may seem a little crazy to use the slow cooker when you have to transfer it to a bowl to add the bread and melt the cheese and on top and use a skillet to caramelize the onions. But, trust me, the soup is so flavorful after 9 hours in the slow cooker. Cooking it low and slow really lets the flavors develop and gives it a richness that you wouldn’t get from a stovetop soup, unless it was on the stovetop for hours and nobody has time to man the stove that long.
You can see if your slow cooker has a sauté option which may help eliminate the need to sauté the onions on the stove first.

French Onion Soup is French because its origins can be traced back to 18th century France. It typically consists of beef broth, caramelized onions, and either stale bread or croutons topped with melted cheese. Traditional recipes also often include brandy, garlic, thyme, bay leaves and other spices. This savory soup is a popular dish around the world and has been adapted to many different cultures’ tastes.

The main difference between onion soup and French onion soup is that the French version is usually made with beef broth or stock, while regular onion soup can be made with either beef or chicken broth. Additionally, French onion soups are typically served with a crust of bread and melted cheese on top while regular onion soups often don’t traditionally use those toppings.

A dry white wine, such as a Sauvignon Blanc or Pinot Grigio, is the best choice for French Onion Soup. The acidity of the wine helps to balance out the sweetness from the onions and compliments the savory flavors in the soup. In addition, white wine won’t overwhelm or change the flavor of your soup like red wines can. If you prefer to use a red wine, then go with a light-bodied variety like Pinot Noir. We used cooking sherry as that’s a common ingredient in an American French Onion soup.

If you like it really thick, the best way to do that is by stirring in a mixture of cornstarch and cold water (it’s called a slurry.) In a small bowl, mix together 1 Tablespoon of cornstarch with 1 Tablespoon of cold water until combined. Then, add this mixture to the soup and stir until it thickens. You can also add small pieces of butter or cream for additional thickness if desired.

Instead of shredded Gruyere, you can use sliced. I recommend at least 2 slices per serving. If you rather not use Gruyere, try Swiss or provolone in its place.

Once the soup has cooked in the slow cooker, you can transfer it to a broiler safe, oven safe bowl or small skillet. If it’s not rated as safe for broiler use, it may crack or damage the bowl when you go to melt the cheese.
If you don’t have a safe bowl, just melt the cheese directly on the sliced baguettes in the oven then put them on top of the individual serving bowls. 

I think it really adds depth to this soup. But, if you want to swap it out, try apple cider vinegar. It will give it just enough tang to really give that dynamic flavor without making it taste like a separate ingredient. Or you can just omit the ingredient altogether.

Leftover soup can be stored in an airtight container in the fridge for up to 5 days.

Yes! You can freeze this delish soup for up to 3 months in a freezer safe container.