Heat olive oil and butter in a large Dutch oven or heavy-bottomed pot over medium heat.
Add the diced onion and sauté for 5–7 minutes until translucent and soft.
Add the minced garlic and tomato paste; cook for 1 minute while stirring constantly to prevent burning.
Pour in the crushed tomatoes, broth, Italian seasoning, red pepper flakes, sugar, salt, and pepper.
Bring the mixture to a gentle boil, then reduce heat to low and simmer for 10 minutes to allow the flavors to meld.
Add the refrigerated tortellini to the pot and increase heat to medium. Simmer for 3–5 minutes (or according to package instructions) until the pasta is tender and floats.
Reduce heat to low and stir in the heavy cream and grated Parmesan cheese until fully incorporated and the cheese has melted.
Add the baby spinach and stir for 1 minute until just wilted.
Remove from heat and serve immediately, garnished with additional Parmesan or fresh basil if desired.