To prepare a spinach tortellini with creamy mushroom sauce pasta recipe, you will first need to prepare the spinach. You can buy fresh spinach at your local grocery store, or you can purchase frozen spinach from the frozen section of the store. If you don't want to buy spinach, use dried spinach that has been thawed. To make the sauce, mix together the cream of mushroom soup, butter, Parmesan cheese, and salt and pepper to taste. Pour the mixture over the pasta and toss to coat.