01 -
Soak breadcrumbs in milk for 5 minutes. In a large bowl, combine the soaked breadcrumbs with ground beef, parsley, thyme, herbes de Provence, salt, pepper, minced onion, minced garlic, ¼ cup Gruyere cheese, and the whisked egg. Mix gently.
02 -
Shape the mixture into 2-tbsp-sized meatballs and chill for 15 minutes to firm up.
03 -
Heat 2 tbsp olive oil in a skillet over medium heat. Brown the meatballs on all sides for 8-10 minutes. Remove from skillet and set aside.
04 -
In the same skillet, add the remaining olive oil and butter. Sauté sliced onions with salt and pepper over medium heat, stirring frequently, until caramelized (20-25 minutes).
05 -
Add garlic, herbes de Provence, and dried thyme to the onions. Stir well. Deglaze the pan with sherry or white wine, cooking until reduced.
06 -
Stir in flour and cook for 1 minute. Gradually whisk in beef stock, simmering for 5 minutes until the sauce thickens.
07 -
Return the meatballs to the skillet, nestling them in the onion sauce. Top with shredded mozzarella and the remaining Gruyere cheese.
08 -
Place the skillet under a broiler and cook for 5-7 minutes, until the cheese is melted, bubbly, and golden brown.
09 -
Garnish with fresh thyme leaves and serve hot with crusty bread or over mashed potatoes.