1 pound assorted mushrooms, sliced - I prefer cremini
4 strips bacon, cooked and crumbled
1/2 cup milk
1/2 cup heavy cream
3 large eggs
2 egg yolks
Pinch of freshly grated nutmeg
Salt and freshly ground pepper
6 ounces gruyere cheese, grated (1 1/2 cups)
How to make it
On a lightly floured surface, roll dough into a 12-inch circle, or, press the pastry dough into a tart pan pr pie plate, pressing the dough into the corners. Transfer to fridge to chill for 30 minutes.
Preheat oven to 350°. Line the pastry with parchment paper, wax paper, or aluminum foil, pressing into the corners and edges. Fill at least two-thirds with baking weights -I use dried beans.
Bake first for 10 minutes, remove from oven and let cool a few minutes. Carefully remove parchment paper and weights. Poke the bottom of the pie pan with the tongs of a fork and return to oven and bake an additional 10 minutes or until lightly golden. Transfer to a wire rack to cool while making filling.
Heat butter in a large nonstick skillet over medium high heat. Add onions and shallots, and cook, stirring, until brown - we want them to caramelize a bit. Add mushrooms. Cook, stirring frequently, until mushrooms first release their liquid and then liquid evaporates and mushrooms are dark golden brown, 8 to 10 minutes.
Place tart pan on a baking sheet. Sprinkle half the cheese evenly over the bottom of the crust. Spread mushroom-onion mixture over the cheese, sprinkle the crumbled bacon on top and then top with remaining cheese.
In a medium bowl, whisk together milk, cream, eggs and egg yolks. Season with nutmeg, salt, and pepper. Pour over the filling, making sure it spreads out and covers everything.
Bake until just set in the center, 30 to 35 minutes. Cool on a wire rack for about 10 minutes before slicing.