Easy Homemade Chicken Meatballs - a hint of rosemary

Ingredients

• 1 pound ground chicken
• 1 pound mild Italian chicken sausage ((casing removed))
• 1 1/2 cups fresh white bread crumbs
• 3 garlic cloves, minced
• 1/3 cup chopped fresh parsley
• 1/2 cup freshly grated pecorino romano cheese ((2 ounces))
• 1/2 cup freshly grated parmesan cheese ((2 ounces))
• 1/4 cup milk
• 2 extra-large eggs, lightly beaten
• 1 teaspoon salt
• 1/2 teaspoon freshly ground black pepper
• 1/2 cup extra-virgin olive oil
• 1 medium onion, finely chopped ((5 ounces / 1 cup))
• 2 garlic cloves, minced
• 1 stalk celery, finely chopped ((2 ounces / 1/2 cup))
• 1 carrot, peeled and shredded ((4 ounces / 1 cup))
• pinch of chopped fresh thyme
• 1/2 teaspoon salt
• 2 - 28 ounce cans plum tomatoes
• 2 bay leaves
• handful of celery leaves (optional)
• 1/2 cup freshly grated pecorino romano cheese