Kittencal's Spinach & Four-Cheese Manicotti (Vegetarian)

I have been making this recipe for years, it is *the best* manicotti recipe hands down! --- I have made this many times for dinner parties and have made it for socials and large gatherings increasing amounts of coarse, I have even served this at my Thanksgiving and Christmas holiday table as an extra dish along with a turkey or ham --- to save time I always mix up the filling a day ahead and refrigerate this will also give the flavors a chance to blend together, or you may prepare up to step #9 cover and refrigerate for up to 24 hours --- don't forget to cook the spinach first before using for this recipe