Place a large Dutch oven over medium-high heat. Add the beef sausage and cook, breaking it into small crumbles with a wooden spoon, until browned and fully cooked (approximately 6-8 minutes).

Reduce heat to medium. Add the diced onion to the pot with the sausage. Sauté for 4-5 minutes until the onion is translucent and soft.

Add the minced garlic, Italian seasoning, and red pepper flakes. Cook for 1 minute until fragrant.

Sprinkle the flour over the sausage and vegetable mixture. Stir constantly for 1-2 minutes to cook out the raw flour taste and create a light roux with the rendered fat.

Slowly whisk in the beef broth and crushed tomatoes, scraping the bottom of the pot to deglaze any browned bits (fond).

Bring the liquid to a gentle simmer. Reduce heat to low and let the flavors meld for 10 minutes.

Add the refrigerated tortellini to the simmering broth. Cook according to package directions, typically 3-5 minutes, until tender but still holding shape.

Stir in the fresh baby spinach and heavy cream. Continue to stir until the spinach is wilted and the soup is heated through.

Turn off the heat. Stir in the grated Parmesan cheese until melted and incorporated.

Adjust seasoning with kosher salt and black pepper before serving in warmed bowls.