Grease a 9-inch springform pan and line the bottom with parchment paper
In a bowl, stir together your flour, salt, pepper, and oregano. Using two butter knives, held against each other with one in each hand to form an “X,” cut your butter into your dough, with the knives pulling away from each other and back in, until you have a sand-like consistency
Add in your water (I like to put a few ice cubes in a glass before filling it with cold water to make sure it’s extra cold), stir together, and then compress the dough into a ball. See notes below if you have a food processor!
Place your dough between two large pieces of parchment paper, and roll to ⅛” thickness, making sure your dough is an even thickness throughout
Gently peel the parchment back from the top layer, lay it back onto the dough, flip all of it over, and repeat with the bottom (now top) layer of parchment
Removing one side of the parchment, carefully lay that side face down into your prepared 9-inch springform and remove the top layer of parchment
Carefully shift the dough to ensure it lies flat within the pan and along the sides. Then fold under the overhanging dough along the rim, to form your crusts edges
Place your pan in the fridge for 15 minutes to allow the butter in your dough to chill
Preheat your oven to 425°F
Once chilled, remove your springform from the fridge and prick the bottom and sides of your crust with a fork to prevent the crust from puffing when you bake. Crinkle a piece of parchment paper and lay it carefully in your pan before pouring in your baking weights. Since you are using a deep pan, you will need more baking weights than usual for this bake. Make sure you have enough weights to reach to almost the top of your crust
Bake your chilled crust for 15 minutes, remove from the oven, and carefully remove the parchment paper and baking weights before returning to the oven to bake an additional 15 minutes, until the inside bottom of your crust is no longer wet-looking and is lightly golden. Cool completely before adding your filling
Preheat your oven to 325°F
Place your frying pan over medium heat, then add your olive oil and minced garlic. Stir for a minute or two until fragrant, then add in your chopped spinach and a dash of salt and pepper, stirring until wilted and most of the water has been cooked out of the spinach. Set aside to cool
Whisk together your milk and cornstarch in a large bowl until the cornstarch is dissolved
Add in your eggs, yogurt, salt, pepper, and a pinch of nutmeg. Use an immersion blender and blend just until combined. You just want to mix together your custard, we’re not trying to add in extra air
Stir in your lemon zest, mozzarella, and feta before folding in your garlic spinach
Place your cooled crust on a baking sheet and pour the filling mixture into your crust. If you notice some spots seem to have more spinach or cheese, use a spoon or knife to lightly swirl those bits to separate them, without touching the crust
Bake for 65-75 minutes, when you tap the side of the pan, the edges will be set and the center will have a very slight wobble to it. You can stick a knife in the center, and it should come out clean
Allow to cool for at least an hour at room temperature in the pan. If the quiche still feels hot through the pan, wait another 30 minutes and feel again. After it’s cooled, use a knife to loosen the sides of the quiche from the pan, open the springform, and place it on a serving plate
Slice and enjoy!