French Onion Chicken Meatballs

Name: French Onion Chicken Meatballs
Prep time: 15 min
Total time: 15 min
Cuisine: American
Ingredients: 2 tbsp. extra-virgin olive oil, for baking sheet; 1 lb. ground chicken; 1/2 c. shredded Gruyère; 1/4 c. bread crumbs; 2 tbsp. freshly chopped parsley; 1 large egg, beaten; 2 cloves garlic, minced; 1 tsp. kosher salt; Freshly ground black pepper; 4 tbsp. butter; 2 large onions, thinly sliced; 2 c. low-sodium beef broth; 2 tsp. freshly chopped thyme, plus more for garnish; Kosher salt; 1 1/2 c. shredded Gruyère