Set a large stock pot over medium heat. Add olive oil, half the garlic, carrot, onion, celery, bay leaf, and thyme and gently saute until fragrant, about 5 to 7 minutes. Pour in chicken broth, add parsley stems, black peppercorns and salt, to taste. Bring to a boil then reduce heat to simmer while you work on meatballs and tortellini.
For the meatballs:
Caramelize the diced onion in a saute pan with a little olive oil over medium heat. Add the sausage, egg, onion, thyme, parsley, and cheese to the bowl of a food processor and pulse until they all come together. Season with salt and pepper. Heat a skillet with a few tablespoons of olive oil until just smoking. Use a small ice cream scoop to drop meatballs onto skillet. Cook, turning, until golden brown.
Drop tortellini straight from freezer into soup. Cook until they float. Once meatballs are browned, add to pot of chicken broth. Bring to a simmer and cook for 2 or 3 minutes. Give soup a final seasoning and serve in shallow bowls with a small shower of Parmesan, olive oil, and parsley.