Boil a large pot of water. Add salt, then add the rigatoni. Cook according to the directions on the box.
Before draining the pasta, reserve 1 cup of the pasta water.
While the pasta is in the strainer, add 1/2 cup of pasta water and the Boursin cheese to the pot. Cook over medium-low heat and stir until the cheese is melted and mixed with the pasta water.
Stir in the rigatoni and spinach. Cover with a lid and let cook for 2 minutes.
Remove the lid and add the salt. If the sauce is no longer creamy add more of the pasta water, 1/4 cup at a time.
Optional: Top with crushed red pepper flakes and fresh cracked black pepper.