To make the flaky pastry crust, in a food processor, combine the flour, salt, and baking powder—pulse for a few seconds, just enough to mix well. Add the butter and pulse several times until the flour resembles coarse cornmeal. Slowly add the water with the motor running. Stop as soon as you have added the last drop of water. Don't worry; the dough will not be fully mixed at this point.
Turn the dough out onto a lightly floured work surface and mix it by hand until it comes together into a ball. Place in a large zip-top bag and refrigerate for at least 2 hours or overnight.
Lightly flour your work surface. Roll the dough out into a giant circle, about 15 inches round and 1/8 inch thick. To transfer it to a 9-inch springform pan, coil it around your rolling pin. Unwind the dough loosely over the pan. Gently push the dough down into the corners, leaving at least 1inch of dough hanging over the top edge. The outer-upper lip of the springform pan has a curled edge facing outward. Pinch the excess dough tightly around the edge, leaving any excess dough hanging down the outside. It is important to pinch as firm as possible without tearing the dough. This will prevent the crust from shrinking. Refrigerate the crust for 2 hours or more.
Preheat the oven to 350°F (175°C). Transfer the pan to a baking sheet. Situate the baking sheet in the lower third of the oven - bake for 10 minutes. Pull the baking sheet out of the oven and use a serrated knife to cut along the pan's top edge. All the scraggly pastry pieces that were pinched into place will fall off.
To make the basic quiche filling, whisk the eggs, yolks, cream, salt, pepper, and nutmeg together in a large bowl. When the crust is done, increase the oven temperature to 375°F (190°C).
Pour the filling into the pre-baked crust and bake until the filling is firm, about 50 minutes. Let it cool for about 30 minutes before cutting. It needs time to set. You will notice the difference resting makes, then you can slice it.