Slow Cooker French Onion Meatballs

Slow Cooker French Onion Meatballs bring everything you love about classic French onion soup into one cozy, irresistible dish. First, tender meatballs slowly simmer in a rich caramelized onion sauce, and then they’re finished with melted Gruyère and mozzarella for a comforting, restaurant-style experience at home. Because the slow cooker does all the work, this recipe fits effortlessly into busy days, yet still feels indulgent and special.

Historically, French onion soup dates back centuries, prized for transforming humble onions into something luxurious. Similarly, this modern twist captures that same magic, but in a shareable, crowd-friendly form. As the onions slowly cook, their natural sweetness deepens, while the beef broth and herbs create balance and warmth.

Whether you’re hosting friends, planning game-day bites, or simply craving something hearty, these meatballs deliver bold flavor without complexity. Most importantly, they’re comforting, reliable, and guaranteed to disappear fast.

Recipe Yield: 6 servings

INGREDIENTS

1 lb frozen beef meatballs
2 large yellow onions, thinly sliced
1 cup shredded Gruyère cheese
½ cup shredded mozzarella cheese
2 cloves garlic, minced
1 Tbsp all-purpose flour
1 cup beef broth
2 Tbsp butter
1 Tbsp Worcestershire sauce
1 tsp fresh thyme leaves
½ tsp salt
½ tsp black pepper
Fresh parsley, finely chopped (for garnish)

INSTRUCTIONS

1. Caramelize the onions:
First, melt the butter in a large skillet over medium heat. Add the sliced onions and cook, stirring often, for 18–22 minutes until deeply golden and caramelized. Then, add the garlic and cook for 30 seconds until fragrant.

2. Build the onion sauce:
Next, sprinkle the flour over the onions and stir well to coat. Gradually pour in the beef broth while stirring continuously. Add Worcestershire sauce, thyme, salt, and black pepper. Simmer for 2–3 minutes until slightly thickened.

3. Assemble in the slow cooker:
Meanwhile, place the frozen meatballs into the slow cooker. Pour the warm French onion sauce evenly over the top, ensuring the meatballs are well coated.

4. Slow cook to perfection:
Cover and cook on LOW for 4–5 hours or on HIGH for 2–3 hours, until the meatballs are tender and infused with flavor.

5. Add cheese and finish:
Finally, sprinkle Gruyère and mozzarella over the meatballs. Cover and cook an additional 10–15 minutes, until melted and irresistibly gooey. Garnish with fresh parsley before serving.

Helpful Tips to Perfect This Recipe

• Deep onion flavor matters:
  Take your time caramelizing the onions, because slow browning develops the signature French onion richness that defines this dish.
• Use quality cheese blends:
  Gruyère brings classic depth, while mozzarella adds meltability, creating a silky, restaurant-style finish.
• Serve it strategically:
  These meatballs shine over mashed potatoes, toasted baguette slices, or buttered noodles for a complete, comforting meal.