To prepare the crust

1. In the bowl of a food processor, mix flour, sugar and salt to combine. Add cold butter and pulse until butter is pea sized.
2. Add 3 tablespoons of ice water and pulse to combine. Add 1 to 2 additional tablespoons of ice water one tablespoon at a time (pulsing after each addition) as needed just until the dough comes together. Do not over mix.
3. Form the dough into a flat oval and wrap in plastic. Chill for at least 30 minutes.
4. When you are ready to bake, preheat the oven to 450 degrees.
5. Roll out the chilled dough to fit a deep dish pie plate and crimp the edges. (See How to Blind Bake a Pie Crust in our How-To’s section.)
6. Partially bake the pie crust for 8-9 minutes, making sure you weigh the bottom of the crust down with pie weights or dried beans so that it does not puff up as you bake it. Allow to cool slightly.

To prepare the filling

1. Defrost the spinach and drain well. You can let it sit overnight to defrost in the refrigerator or you can defrost it in the microwave. Either way, it is important to get all of the water out of the spinach. After it has drained, wrap the spinach in a few layers of paper towel and squeeze to remove the last remaining moisture.
2. After partially baking your pie crust, reduce the oven to 425 degrees.
3. Place the onion in a small pan and sauté with the butter until the onions are soft and translucent. Cool slightly.
4. Sprinkle the drained spinach and sautéed onion evenly into the bottom of the partially-baked pie crust. Sprinkle the shredded cheese on top of the spinach and onions.
5. In a bowl, beat the eggs. Add cream, salt, nutmeg and cayenne pepper and whisk to fully combine the custard mixture. Pour or ladle the custard over the spinach and cheese.
6. Bake at 425 degrees for 15 minutes. Lower the oven heat to 350 degrees and bake for 20-25 minutes more, or until a knife inserted into the center of the quiche comes out clean.
7. Let cool until the quiche sets up a bit (about 30 minutes) and serve in wedges.