Cook rigatoni according to package instructions and set aside 2 cups of pasta cooking water before draining
Melt butter in a large pot or dutch oven
Add the minced garlic and diced onion and cook around 5 minutes, until softened
While the garlic and onion cook, drain and chop the artichokes and chop up the spinach and set aside.
Add the cream cheese, reserved pasta water, and fresh parmesan. Whisk for 5 - 10 minutes, until melted. Whisk in 2 tablespoons of cornstarch, to thicken the sauce.
Stir in the cooked rigatoni, chopped spinach, and chopped artichokes. Stir to combine. Salt and pepper to taste.
Transfer the spinach artichoke pasta to a greased 9 X 13 baking dish
Top with the mozzarella cheese
Bake at 425 degrees for 15 - 20 minutes, until cheese starts to brown on the top and is bubbly