I put this together on short notice Friday night, going from "Preheat oven" to "insert quiche into said oven" in about 20 minutes. I had nothing prepped before I started. I'm pretty proud of that, actually.
1) Preheat oven to 400F.
2) THE CRUST, part I. In a food processor, combine 1 cup flour, a pinch of kosher salt and 1/4 stick COLD butter, cubed. Pulse until thoroughly crumbed, then add another 1/4 stick of butter and repeat. Move to narrow, high-sided bowl and cut in 1/4 c. cold 2% milk (I used a table knife). The dough will seem very crumbly and not quite wet enough; this is okay. Shape it into a ball with your hands, cover the bowl with a paper towel, and set aside.
3) THE FILLING, part I. Chop four pieces of turkey bacon and begin to saute in a buttered skillet. Chop one half of a large white onion and add to the bacon. Chop one cup crimini mushrooms and add to skillet. Stir occasionally. Grate three ounces cheddar and three ounces gruyere cheese. Set aside. When mushrooms are almost cooked, remove skillet from heat, add four cups fresh baby spinach, cover and set aside.
4) THE CRUST, part II: Shape dough into a disc and place on a floured board. Roll to about 1/8" thickness and lay into a 9" pie dish (glass is preferred). Adjust/trim edges as needed. Set aside.
5) THE FILLING, part II. Combine four eggs and one cup 2% milk. Beat until thick and creamy. In a separate bowl, toss the bacon, onion, mushrooms and spinach with the grated cheese and arrange in crust. Cover with custard and place in oven for 35 minutes, or until a knife blade in the center comes out clean. Let sit for at least 10 minutes before serving. Enjoy!