Bring a large pot of salted water to a boil. Add the pasta and cook it until it is al dente, about 10 minutes.
Drain the pasta, return it to the pot then add the sour cream, and stir to combine.
Stir in the artichoke hearts, diced chicken and sundried tomatoes then set the pasta aside.
In a large heavy-bottomed saucepot set over medium heat, melt the butter. Once the butter has melted, add the spinach and cook, stirring, until the spinach is wilted and most of the liquid has cooked off, about 10 minutes.
Stir in the flour then add the milk, garlic powder, white pepper and cream cheese, stirring to combine. Continue cooking the sauce, stirring occasionally, until it thickens slightly, about 5 minutes.
Stir in the grated Parmesan cheese and the white cheddar cheese.
Pour the cheese sauce over the pasta mixture, stirring until well combined then serve.
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