Place a large pot of salted water over high heat and bring to a boil. Cook the rigatoni according to package instructions. Drain and set aside, reserving 1 cup of salty pasta water.
Meanwhile, set a large skillet over medium heat. Add the butter, onions, and garlic. Saute for 2-3 minutes, then add the milk and bring to a boil. Once the milk is scalded add the cream cheese and break it up with a wooden spoon. Whisk the cream cheese until smooth, then add the artichoke bruschetta, spinach, and crushed red pepper. Stir well.
Now mix in the pasta. Add 1/2 to 1 cup salty pasta water and stir well. Simmer another 2-3 minutes while the sauce thickens, then salt and pepper to taste. Garnish with parmesan cheese.