Cook sausage. In a large pot or Dutch oven, heat 2 tablespoons of vegetable oil over medium heat. Then, add the sausage and cook until browned and no longer pink in the middle, breaking it into smaller pieces with a spoon as it cooks. Transfer the sausage to a paper towel-lined plate using a slotted spoon and set aside.
Cook onion, garlic, and flour. Add the rest of the oil to the pot, along with the sausage fat. If needed, add more oil to make it 2 tablespoons in total. Lower the heat to medium-low, put in the chopped onion, and cook for 7-10 minutes until the onion is see-through and soft, stirring now and then to avoid burning. Next, add the minced garlic and cook for an extra 1-2 minutes. Stir in the flour and cook for 2-3 more minutes to make a roux.
Add liquids. Add the crushed tomatoes, chicken broth, thyme, salt, and pepper. Turn up the heat and let it all come to a boil.
Cook tortellini. Put the cheese tortellini in the boiling soup and cook for 3-5 minutes following the instructions on the package until the tortellini are soft.
Combine the ingredients. Remove the pot from heat. Stir in the chopped spinach and the cooked sausage. Mix in the heavy whipping cream, grated Parmesan cheese, and chopped parsley.
Serve. Ladle the soup into bowls. Garnish with additional Parmesan cheese and fresh basil, if desired. Serve hot and enjoy!