Ingredients
For the Meatballs:
- Ground beef: 1 ½ pounds of 80/20 ground beef works best for moist, flavorful meatballs.
- Breadcrumbs: ½ cup of plain or seasoned breadcrumbs helps bind the mixture and adds texture.
- Egg: 1 large egg, lightly beaten, acts as a binder to keep the meatballs together.
- Parmesan cheese: ¼ cup grated Parmesan adds a touch of saltiness and richness.
- Garlic: 2 cloves, minced, infuses the meatballs with aromatic flavor.
- Worcestershire sauce: 1 teaspoon deepens the flavor profile with a hint of umami.
- Onion powder: 1 teaspoon for an extra punch of onion flavor.
- Dried parsley: 1 teaspoon for a touch of freshness.
- Salt and black pepper: ½ teaspoon each, to season the meatballs perfectly.
For the French Onion Sauce:
- Onions: 2 large onions, thinly sliced, are the star of the show, lending sweetness and depth to the sauce.
- Butter: 2 tablespoons unsalted butter for caramelizing the onions to perfection.
- Sugar: 1 teaspoon (optional) helps accelerate caramelization and adds a subtle sweetness.
- All-purpose flour: 1 tablespoon, for thickening the sauce.
- Beef broth: 2 cups, creating the base of the savory sauce.
- Worcestershire sauce: 1 tablespoon, enhancing the richness of the broth.
- Dried thyme: ½ teaspoon for a hint of herbal flavor.
- Gruyère or Swiss cheese: 1 cup shredded, melted into the sauce for a luxurious, cheesy finish.
Step-by-Step Instructions
Step 1: Prepare the Meatballs
Mix the Meatball Ingredients
In a large mixing bowl, combine the ground beef, breadcrumbs, egg, Parmesan cheese, minced garlic, Worcestershire sauce, onion powder, dried parsley, salt, and black pepper. Use clean hands or a spoon to gently mix the ingredients until just combined. Avoid overmixing, as it can result in dense meatballs.
Shape the Meatballs
Using a cookie scoop or tablespoon, portion out the meat mixture and roll it into 1-inch meatballs. This size ensures the meatballs cook evenly and remain tender. Place the formed meatballs on a parchment-lined baking sheet.
Sear the Meatballs (Optional)
While not mandatory, browning the meatballs in a skillet before slow cooking adds flavor and helps them hold their shape. Heat a tablespoon of oil in a skillet over medium-high heat and sear the meatballs on all sides, about 2–3 minutes per side. Once browned, transfer the meatballs to a plate and set them aside.
Step 2: Caramelize the Onions
Slice and Prep the Onions
Thinly slice the onions into even pieces. This ensures they cook uniformly and caramelize beautifully.
Caramelize the Onions
In the same skillet used for the meatballs, melt the butter over medium heat. Add the sliced onions and a pinch of salt. Cook, stirring occasionally, for 20–25 minutes until the onions turn golden brown and caramelized. If you’re short on time, adding 1 teaspoon of sugar can speed up the caramelization process.
Thicken the Sauce
Once the onions are caramelized, sprinkle the flour over them and stir for 1 minute to remove the raw flour taste. Gradually pour in the beef broth while whisking to create a smooth sauce. Stir in Worcestershire sauce and dried thyme, allowing the mixture to simmer for 2–3 minutes until slightly thickened.
Step 3: Assemble the Casserole
Layer the Ingredients
Place the meatballs in the bottom of your slow cooker. Pour the French onion sauce over the top, ensuring the meatballs are evenly coated.
Cook in the Crock Pot
Cover the slow cooker with the lid and cook the meatballs on low for 4–6 hours or high for 2–3 hours. The slow cooking process allows the flavors to meld and the meatballs to become incredibly tender.
Step 4: Add the Cheese
Melt the Cheese
In the final 10–15 minutes of cooking, sprinkle the shredded Gruyère or Swiss cheese over the meatballs. Cover the slow cooker and let the cheese melt into the sauce, creating a creamy, indulgent finish.
Step 5: Serve and Enjoy
Garnish and Plate
Sprinkle chopped fresh parsley over the top for a pop of color and a hint of freshness. Serve the meatballs over mashed potatoes, egg noodles, or rice, or alongside crusty bread to soak up the sauce.






