This is a family recipe that can easily be adapted to suit tastes. For example, you can use chopped spinach instead of broccoli, omit the mushrooms, add bits of chopped cooked ham, etc. I have been making this for years and it is a favorite in our house.
Preheat oven to 350 degrees. Line a standard cookie sheet with foil. Place the pie shell on the cookie sheet. (The filling may overflow during baking)
In a large skillet on medium heat, melt the butter. Add the chopped onion and saute for 2-3 minutes. Add the mushrooms and chopped broccoli. Saute 7-10 minutes until tender. Set aside.
In a large bowl, add the heavy cream, eggs and cheese. Mix thoroughly. Add a pinch of nutmeg. You may also want to add 1/8 tsp black pepper and a little salt. Mix in the sauteed vegetables. Blend thoroughly. Pour into the pie shell and sprinkle top with 1/4 cup grated parmesan cheese. Bake 45-50 minutes until center is firm and pie is golden brown.