This is technically a Medieval recipe, from Le Menagier de Paris.
"MUSHROOMS of one night are the best, and are small and red inside, closed above: and they should be peeled, then wash in hot water and parboil; if you wish to put them in pastry, add oil, cheese and powdered spices."
So here is what I did:
1 recipe of pie crust
about 1 cup fresh mushrooms, whole or sliced depending on size
1 tsp olive oil
1 tbs mature cheddar cheese, finely chopped or shredded
Make the pie crust and lay it in a large ramekin or small casserole dish or pie plate. Preheat oven to 375 f (200 c) Fill a small saucepan 3/4 with water and heat to boiling. Take the mushrooms and parboil them for a few minutes, just to get them heated and slightly softened. Drain the water. Stir the oil, spices and cheese into the drained mushrooms and pour the mixture into the pie crust. Bake 10 - 15 minutes or until crust is golden brown on edges.
I think if I made this again I'd skip the parboiling of the mushrooms (I don't really know what purpose it serves here. An 18th century mushroom recipe that follows similar instructions says it's to "take off the faintness" -- maybe it's a holdover from the days when you might be eating poisonous ones? Some kinds of food are poisonous if eaten raw but if they're first boiled they become healthy.)