Melt the butter in a large pot over medium heat. Add the ground beef and cook until well browned. Ensure the meat reaches a safe internal temperature of 160°F (71°C). Drain any excess fat from the pot.
Stir the onion, garlic, carrots, and celery into the beef. Cook for 5 minutes until the vegetables soften.
Add the cherry tomatoes, Italian seasoning, paprika, dried basil, red pepper flakes, and bouillon cubes. Cook for 6 minutes until the tomatoes soften and release their juices.
Stir in the tomato paste and cook for 1 minute. Pour in the beef broth and 1 cup (240 ml) of water. Add the bay leaf. Bring the liquid to a boil, then lower the heat and simmer for 10 minutes.
Add the tortellini to the pot. Cook according to the package directions, usually 5 to 7 minutes.
In a small bowl, whisk the cornstarch and 2 tablespoons of cold water together. Stir this mixture into the soup and simmer for 2 minutes until the broth thickens slightly.
Turn the heat to low. Stir in the heavy cream and spinach. Heat gently until the spinach wilts. Remove the bay leaf.
Taste the soup and season with brown sugar, salt, and black pepper. Serve warm with grated Parmesan and fresh basil.