Make the Meatballs:

• In a large bowl, soak breadcrumbs in milk for 5 minutes.

• Add ground beef, parsley, fresh thyme, herbes de Provence, salt, pepper, minced onion, pressed garlic, half of the Gruyere cheese, whisked egg, and mozzarella. Mix gently until combined.

• Shape mixture into 1½-inch meatballs and place on a baking sheet. Refrigerate while preparing the sauce.

Prepare French Onion Sauce:

• Heat 2 tbsp olive oil and 2 tbsp ghee or butter in a large skillet over medium heat.

• Add sliced onions and season with salt and pepper. Cook, stirring frequently, until onions are deep golden brown and caramelized (about 25-30 minutes).

• Add garlic, herbes de Provence, and dried thyme. Cook for another minute until fragrant.

• Pour in sherry or white wine, scraping the bottom to deglaze the pan. Let the liquid reduce by half.

• Sprinkle flour over the onions, stirring constantly to avoid lumps, cook for 2 minutes.

• Slowly add beef stock while stirring, bring to a simmer, and cook until sauce thickens slightly.

Cook the Meatballs:

• In a separate skillet, heat remaining 2 tbsp olive oil over medium-high heat.

• Add meatballs and cook, turning occasionally, until browned on all sides and cooked through (about 10-12 minutes).

Combine and Serve:

• Transfer meatballs to the onion sauce and stir in remaining Gruyere cheese.

• Simmer together for 5 minutes to meld flavors and melt the cheese.

• Garnish with fresh thyme leaves before serving.