Description
This Slow Cooker French Onion Soup is a comforting classic with deeply caramelized onions simmered in rich beef broth, enhanced with herbs and a touch of balsamic vinegar. The soup is served with homemade garlic croutons topped with melted Swiss and Parmesan cheeses, creating a warm, hearty meal perfect for cozy nights.
Ingredients
Scale
Main Ingredients
- 1 stick butter
- 5 sweet yellow onions, sliced (white, yellow, or red onions also work)
- 1 tsp salt
- 1/4 tsp pepper
- 1/4 cup flour
- 64 oz beef broth or beef stock (two 32-oz containers)
- 1 tsp sugar (optional, used only if onions aren’t labeled ‘sweet’)
- 2 tsp minced garlic
- 1/4 tsp dried thyme (not ground)
- 1/4 tsp dried oregano (not ground)
- 1 tsp Worcestershire sauce
- 1 Tbsp balsamic vinegar
- 1 bay leaf
For Serving
- 1 baguette
- Olive oil
- 1 whole garlic clove
- Sliced Swiss cheese (can substitute provolone or Gruyere) – about 2 slices per serving
- Shredded Parmesan cheese – about 1 tablespoon per serving
Instructions
- Caramelize Onions: In a large skillet over medium-high heat, melt the butter. Add the sliced onions, then sprinkle with salt and pepper. Sauté, stirring often, until the onions are browned and caramelized, about 10 minutes. Adjust heat to prevent burning.
- Make Onion Roux: Add the flour to the skillet with the butter and onions. Stir and cook for 2 more minutes to form a roux, which will help thicken the soup.
- Transfer to Slow Cooker: Pour the floured onion mixture into the slow cooker. Add beef broth, sugar (if using), minced garlic, dried thyme, dried oregano, Worcestershire sauce, balsamic vinegar, and place the bay leaf on top. Stir everything well to combine.
- Cook Soup: Cook on HIGH for 4 hours or on LOW for 8 hours to allow flavors to meld and onions to soften thoroughly. Remove the bay leaf before serving.
- Make Garlic Croutons: Preheat the oven to 500°F (broil). Slice the baguette into 1/4 inch slices and place them on a sheet pan. Brush each slice with olive oil using a pastry brush. Broil for 3-5 minutes or until the bread is toasted and browned to your liking. Immediately rub the toasted bread with the cut side of a garlic clove to infuse garlic flavor.
- Assemble and Broil Soup Bowls: Pour the hot soup into ovenproof bowls placed in a pie tin or baking sheet. Add homemade garlic croutons or store-bought croutons on top. Layer 1-2 slices of Swiss cheese and sprinkle Parmesan cheese over the croutons. Broil in the oven until the cheese bubbles and browns slightly, creating a delicious melty crust.
Notes
- Freeze leftover soup without the croutons or cheese. Cool completely, then store in freezer-safe bags or containers for up to 3 months.
- To reheat frozen soup, thaw overnight in the refrigerator, then warm on the stovetop or in the microwave.
- Adjust sugar addition depending on the sweetness of your onions; sweet onions may not need extra sugar.
- For vegetarian adaptation, substitute beef broth with vegetable broth and omit Worcestershire sauce or use a vegetarian version.
Nutrition
- Serving Size: 1 cup (about 240ml) of soup without bread and cheese
- Calories: 185
- Sugar: 5g
- Sodium: 780mg
- Fat: 9g
- Saturated Fat: 5g
- Unsaturated Fat: 3g
- Trans Fat: 0g
- Carbohydrates: 18g
- Fiber: 2g
- Protein: 6g
- Cholesterol: 25mg
