Slow-Cooker Caramelized Onions & French Onion Soup | Make Ahead Mondays
This slow-cooker French onion soup brings deep, rich flavor from caramelized onions, hearty broth, and toasted cheesy croutons. Perfect for make-ahead comfort.
Equipment
- 1 Slow cooker
- 1 Broiler
- 1 Knife for slicing onions
Ingredients
Main Ingredients
- 12 Yellow onions small to medium, peeled and thinly sliced
- 3 Red onions medium, peeled and thinly sliced
- 6 tablespoons Olive oil divided, for caramelizing and drizzling
- ½ teaspoon Kosher salt for seasoning
- ½ teaspoon Dried thyme for seasoning
- 1.5 cups Beef broth
- 1.5 cups Chicken broth
- Kosher salt and black pepper to taste
- 6-8 slices French bread 1 to 1.5-inches thick each
- Olive oil for drizzling on bread
- 6-8 slices Swiss cheese thinly sliced or ¼ pound grated
Instructions
Instructions
- Peel and thinly slice all your onions.
- Dump the sliced onions, olive oil, kosher salt, and dried thyme into your slow cooker. Stir it all real good to mix flavors.
- Cover and set your cooker on low for 10 to 12 hours. Stir occasionally for even caramelizing.
- When onions are deep golden and caramelized, pour in the beef and chicken broth. Stir gently to combine.
- Cover again and set the cooker on high for 2 to 3 hours to heat through.
- Season the soup with more kosher salt and black pepper to taste.
- While soup simmers, preheat your broiler. Drizzle olive oil lightly on bread slices and toast under broiler 1–2 minutes per side until golden.
- Ladle hot soup into oven-safe bowls. Top each with a slice of toasted bread and Swiss cheese.
- Place bowls under broiler until cheese is melted and bubbly. Serve hot.
- Store leftovers in airtight containers in fridge up to 4 days or freeze without bread and cheese up to 3 months.
Notes
For best results, use both beef and chicken broth and allow plenty of time for onions to fully caramelize. Toasted bread and melty cheese add incredible flavor and texture.