Cook pasta in boiling water according to package directions.
Meanwhile, in a large skillet, put 1 tablespoon of water and spinach greens. Wilt spinach over high heat, tossing several times to cook evenly. This will take only 3-5 minutes. Remove pan from heat when wilted.
While pasta is cooking, in a heavy saucepan, melt butter over medium heat. Stir in flour, salt, nutmeg and pepper, until smooth. Cook and stir for 15-30 seconds or so. Gradually pour in milk, stirring constantly. Bring to a boil, stirring constantly; cook and stir for 2 minutes. Sauce will thicken.
Remove sauce from heat; stir in Parmesan cheese until melted, then stir in wilted spinach.
Drain cooked pasta in colander and return pasta to cooking pot. Pour Spinach Alfredo sauce into pasta and stir until pasta is coated. Garnish with additional sprinkled Parmesan cheese if desired.