Add cavatappi noodles to a pot of boiling salted water. Cook al dente according to package instructions (8-9 minutes for cavatappi). Reserve 1 cup of pasta water and drain the rest.
While noodles are cooking, prepare the sauce. In a large skillet over medium heat, add oil. When hot, add shallots and cook until softened (3-5 minutes).
Add Italian sausage. Cook, breaking up the meat with a wooden spoon and stirring occasionally until the sausage is browned and cooked through (about 10-12 minutes).
Add garlic and cook for 1 more minute, or until fragrant.
Add sun-dried tomatoes, tomato paste, oregano, paprika, garlic powder, salt, pepper, and red pepper flakes. Stir to combine.
Add reserved pasta water. Stir to combine, scraping the brown bits off the bottom of the pan as you go. Add heavy cream, sour cream, parmesan, and mozzarella cheese. Stir to combine.
Add spinach, stirring to combine. Simmer until cheese is fully melted and spinach is wilted (5-7 minutes). The sauce will thicken slightly.
Add the cooked pasta; toss to coat.
Serve topped with more parmesan cheese and fresh parsley. Add salt and pepper to taste.