In a large pot, bring salted water to a boil. Cook the tortellini according to package instructions until al dente. Drain and set aside, reserving 1/2 cup of pasta water.
In a large skillet, heat the olive oil over medium heat. Add the minced garlic and sauté for about 1 minute, until fragrant, being careful not to burn it.
Pour the heavy cream into the skillet and stir well to combine with the garlic. Let it simmer for about 2-3 minutes, allowing it to thicken slightly.
Stir in the pesto and grated Parmesan cheese. Mix until the cheese is melted and the sauce is creamy. If the sauce is too thick, gradually add reserved pasta water until you reach the desired consistency.
Add the halved cherry tomatoes and chopped spinach to the sauce. Cook for another 2-3 minutes until the spinach wilts.
Toss in the cooked tortellini, ensuring they are well coated with the creamy pesto sauce. Season with salt, pepper, and red pepper flakes (if using) to taste.
Remove from heat and let it rest for a minute. Serve immediately, garnished with fresh basil leaves.
Notes
Feel free to adjust the amount of pesto based on your taste preference.