To prepare the pesto, add the fresh basil leaves, baby spinach, grated Parmesan cheese, roasted cashews, and minced garlic to the bowl of a food processor. Pulse the mixture until the ingredients are finely chopped and well combined. You may need to scrape down the sides of the bowl with a spatula to ensure everything is mixed evenly. Then, while the food processor is running, drizzle in the olive oil and mix until the pesto turns into a smooth and cohesive paste. Transfer the pesto to a small mixing bowl and stir in the heavy cream until fully incorporated. Season the pesto with salt and black pepper.

Bring a large pot of water to a rolling boil. Meanwhile, slowly and gently heat the pesto in a large skillet over low-medium heat, stirring occasionally. Make sure that the pesto is evenly heated through, but don’t let it come to a boil. Gentle heating helps maintain the sauce's smooth and creamy texture, as well as its fresh taste and vibrant color.