Mushroom and Caramelized Onion Quiche

Directions

1. Mix the all-purpose flour, white whole-wheat flour, and salt together in a bowl. Work the butter cubes into the flour with your hands until the mixture starts to become sandy and the butter pieces are between the size of a lentil and half of a walnut. Make sure that you don’t allow the butter to become too warm.
2. Mix water into the dough a couple of tablespoons at a time with your hands or a spatula. Take care not to completely mix the butter into the dough; you want to leave small pieces. When the dough starts to come together, squeeze a piece in your palm; if it sticks together, the dough is hydrated enough. If it crumbles, continue adding a little bit of water at a time until you can form a ball. Pat the dough into a disc, wrap tightly in plastic wrap, and refrigerate for at least 1 hour.
3. Melt 2 tablespoons butter in a skillet over medium-high heat; add onions and toss to coat in butter. Sprinkle a generous pinch of salt over the onions and stir. Cook the onions until they begin to become slightly translucent, 3 to 5 minutes. Reduce heat to medium-low and continue cooking while stirring frequently until they have are a rich golden brown color and taste very sweet, 45 to 60 minutes.
4. Heat 1 teaspoon olive oil in a separate skillet over medium heat; add mushrooms, thyme, and ½ teaspoon salt. Cook and stir the mushrooms until they have released a lot of liquid and reduced in size, 5 to 7 minutes; remove with a slotted spoon to a paper towel-covered plate.
5. Beat eggs, egg yolks, milk, heavy cream, 1 teaspoon salt, and a few turns of freshly cracked black pepper together in a bowl.
6. Remove dough from the refrigerator and allow to sit at room temperature for about 10 minutes. Lightly flour a flat work surface.
7. Roll dough out into a circle on the prepared surface until large enough to fill a pie plate. Carefully transfer the dough to the pan; trim and crimp the edges. Poke the crust in several spots with a fork. Put pie plate in the freezer while the oven preheats.
8. Preheat oven to 425°F (220°C).
9. Line pie crust with a piece of parchment paper. Put pie weights onto the parchment.
10. Bake in preheated oven until the the edges begin to show color, about 15 minutes.
11. Remove plate from the oven, remove the parchment and weights, and brush egg mixture over the crust. Continue bake until the bottom of the crust begins to show color, 5 to 10 minutes more.
12. Reduce oven temperature to 325°F (165°C).
13. Arrange caramelized onions, mushrooms, and goat cheese in the bottom of the par-baked pie crust. Pour the egg mixture over the vegetables and cheese.
14. Bake until the quiche has puffed up and has only the slightest jiggle in the center, 45 to 55 minutes; cool quiche on a pastry rack to be served at either room temperature or cold.