Brown sausage in a stock pot over medium-high heat; remove sausage with a slotted spoon; set aside.
Add onion and garlic to stock pot and sauté until tender and fragrant (~2 minutes).
Add carrots, celery, Italian seasoning and continue to cook 3 minutes more.
Add broth; bring to a bubbly boil.
Mix water and cornstarch in small container.
Add the cornstarch mixture and half & half; stir until thickening (~2 minutes).
Stir in tortellini and browned sausage; return to a boil, cover and cook 4 minutes.
Stir in spinach, remove from heat; serve immediately.