If you are a spinach lover, then you will have to try this recipe! I have made this many times to serve at a brunch get together (I always make two of these to serve at a brunch!) Plan ahead this dish needs to chill for a minimum of 8 hours or up to 24 hours or until the custard is absorbed in the bread. You can really use any cheese that you wish I find that either asiago or Gruyere are the best! If you don't want a strong spinach taste then use only one box of frozen spinach. To save time make the spinach/mushroom filling up to 1 day in advance and refrigerate, just warm slightly in the microwave before layering in the strata. You will LOVE this!