#1 In a 12-inch cast-iron skillet, melt butter with olive oil over medium-low heat #2 Add onions and garlic cook, stirring occasionally, until softened and lightly browned, about 25 minutes. Stir in flour cook, stirring occasionally, for 5 minutes. Stir in broth, thyme, salt, and pepper add in the meatballs and bring to a boil. Reduce heat simmer until slightly thickened, about 20 minutes #3 Preheat oven to broil. Sprinkle cheese onto meatballs #4 Broil 6 inches from heat until cheese is melted and lightly browned, 3 to 5 minutes. Garnish with thyme, if desired. Serve immediately.