Sauteed mushrooms on onions in some olive oil, then add cream, lots of fresh thyme and parsley, pepper and salt and reduce.
The great thing is that you can make this mixture in advance, so come bake time its just a matter of stretching out the dough, spreading a few good dollops of the mushroom mixture and topping with parmesan and EVO. (and any left over mixture is great with pasta as well)
Over the years this one has rivalled the Margherita in terms of popularity. Even people who previously said that they hate mushrooms, have become converts.