For the crust:
For the filling:
1. In a food processor process flour, salt and cold cubed butter. process until crumbs are formed. Add cold water, process until dough is formed. Do not over mix.
2. Transfer the dough to a work surface, pat into a ball and flatten into a disk. Wrap in plastic and refrigerate for 30 minutes.
3. Meanwhile make the filling: slice the mushrooms and onions. Heat 2 tbsp of olive oil and butter in a large pan. Sauté onion for 4-5 minutes, add crushed garlic, sauté for 1 minute. Add mushrooms, cook until the mushrooms release all of their moisture, and get well browned, about 10 minutes. Add more oil if needed. Remove from heat and set aside.
4. In a large bowl beat eggs, heavy cream, salt, pepper, dried oregano and nutmeg. Set aside.
5. Roll out the dough on a lightly floured board. Lightly dust the top of the dough. Roll until the dough is about 1/8 inch thick. Transfer the dough to a 9-10-inch (24-25cm) pie pan. evenly press the pastry onto the bottom and up the sides of your pan. Trim off the excess dough off the top of the pan. Gently pierce the bottom of the crust with a fork. Transfer to the freezer for 30 minutes.
6. Preheat oven to 350F (175C).
7. Blind baking: line a parchment paper over the dough. Fill with dry beans, rice or pie weights. Bake for 15 min. Remove the weights and the parchment paper. Return to oven for another 10 minutes or until crust is slightly golden. Remove from oven.
8. spread mushroom mixture over the crust, then sprinkle the cheese evenly. pour the eggs and cream mixture.
9. Bake until golden brown and set, about 30 minutes. Allow to cool before serving.