• Preheat oven to 375° F.

For the Pastry: Food Processor Method

• Place flour and kosher salt in the bowl of your food processor. Pulse a few times to combine.
• Add cold cubed butter to flour mixture and pulse several times, just until there are no pieces larger than a pea remaining.
• In a small bowl, mix an egg yolk with 3 tablespoons of iced water. Add the egg mixture to the flour mixture and pulse until the dough comes together.
• Take the lid off and pinch a bit of the dough between your fingers. If it holds it shape, it’s ready. If it's too crumbly to hold its shape, add another half tablespoon of cold water and pulse again. Repeat the pinch test until your dough comes together easily. Don't add more than necessary to form a ball; you don't want the dough to be too wet.
• Empty dough onto a work surface and shape lightly into a disc. Wrap tightly in plastic wrap and place in the fridge to chill for 15 minutes.

For the Pastry: By Hand Method

• Place flour and kosher salt in a large bowl and stir to combine.
• Add grated butter to the bowl and combine using a pastry cutter or your hands. Continue until there are no pieces larger than a pea remaining.
• In a small bowl, mix an egg yolk with 3 tablespoons of iced water. Add the egg mixture to the flour mixture and combine.
• Pinch a bit of the dough between your fingers. If it holds it shape, it’s ready. If it's too crumbly to hold its shape, add another half tablespoon of cold water and combine. Repeat the pinch test until your dough comes together easily. Don't add more than necessary to form a ball; you don't want the dough to be too wet.
• Empty dough onto a work surface and shape lightly into a disc. Wrap tightly in plastic wrap and place in the fridge to chill for 15 minutes.

Rolling Out & Blind Baking the Pastry

• Once the dough has chilled, lay it out on a lightly floured surface and begin to roll it out, maintaining its circular shape. Flip it over every few rolls and re-flour your surface as necessary to ensure it doesn't stick.
• Continue rolling the dough until you have a circle that is 12 inches in diameter. You should have about an inch and a half of a border showing on all sides when you place your tin on the center of the dough.
• Transfer the dough to your quiche tin being careful not to stretch or tear the dough. Fold the edges down and check to ensure there are no holes in the crust to prevent leakage. (For visuals and a few tips on this step, see the post and photos above.)
• Place the crust in the freezer for about 15 minutes to firm up.
• Once chilled, line the crust with parchment paper, fill it with pie weights, and blind bake it at 375 for about 15 minutes. Once the time is up, take the crust out of the oven, remove the parchment and pie weights and check on the color. It should have lost its rawness and have a golden hue. If it still looks too pale, stick it back in (without the weights) for another couple of minutes.

For the Filling

• Heat oil in a nonstick pan and sautee onion until soft. Season to taste with kosher salt and black pepper. Set aside.
• In the same pan, sautee spinach until wilted. Season to taste with kosher salt, black pepper, and a pinch of freshly grated nutmeg. Set aside to cool.
• Once cool, drain the water from the spinach to prevent a soggy quiche. You can do this by placing the wilted spinach in a tea towel and squeezing it tightly over the sink. Once dry, chop the spinach roughly and fluff back up. Set aside.
• In a large bowl, whisk together half and half and four eggs and season with 1/2 teaspoon of kosher salt and 1/4 teaspoon black pepper. This should be enough liquid to fill a standard 9-inch quiche tin, and you may even have some left over.

Assembling the Quiche

• Place the quiche tin on a baking sheet. Then spread sauteed onions over the base of the quiche. Cover onions with grated cheese and then top with sauteed spinach.
• Carefully pour egg mixture over the toppings. Be sure not to spill or overfill the shell. The liquid should nearly reach the top edge of the crust, with about 1/4 inch to spare.
• Transfer the baking sheet to the oven to bake for 35-40 minutes. When done, the quiche will be lightly puffed up, golden on top, and will have lost its wobble when you shimmy the pan.
• Set on a cooling rack to come to room temperature, slice, and enjoy!