Layer the ingredients. In a deep braising pan, add the dry mafaldine, red onion, spinach, cherry tomatoes, tomato sauce, garlic, pesto, Italian seasoning, smoked paprika, salt, pepper, butter and olive oil in the order listed. Spread everything into an even layer to help the cooking liquid reach as much of the pasta as possible.
Add the liquids. Pour in the chicken stock and heavy cream, distributing evenly throughout the pan.
Bring to a gentle boil. Place over medium heat and heat until the liquid begins to gently bubble.
Cover and simmer. Cover with a fitted lid and reduce the heat to a gentle simmer.
Check the pasta halfway through. After 8–9 minutes, remove the lid and gently press the softened noodles down into the cooking liquid using tongs or a spatula. Replace the lid and continue simmering until the pasta is tender and most of the liquid has been absorbed, about 15–20 minutes total. Add a small splash of chicken stock if needed.
Finish with Parmesan and lemon. Remove the lid, add the freshly squeezed lemon juice and shredded Parmesan, and gently toss until the pasta is coated in a creamy sauce.
Serve. Enjoy immediately with additional Parmesan, if desired.