Have a glass of ice water standing by and cut the butter into 16 pieces. Place the steel blade into the work bowl of your food processor and add the flour and salt.
Scatter the butter over the flour. Using the pulse function, process until the mixture is crumbly, with visible pieces the size of very small peas.
With the processor running, start adding the ice water through the feed tube in 1 tablespoon increments until the dough gathers into one or two large pieces. Run the processor for an additional 10 to 15 seconds, just long enough for the dough to gather into a ball. Be careful not to over-process.
Remove the dough from the processor and place it on a sheet of plastic wrap. Using your hands, flatten it into a 1/2-inch thick circle. Wrap tightly and chill for about 30 minutes in the refrigerator or 7 to 10 minutes in the freezer.
When the crust is ready to roll, dust both your rolling surface and the top of the dough with flour. Gently roll the dough from the center out, to a diameter of about 13 inches for a 10-inch tart pan, dusting with a little additional flour as you go along.
To move the dough into the tart pan, carefully roll it around the rolling pin, then unroll it over the pan. Using your fingertips, press the dough firmly into the pan, being sure to form it into the edges and flutes. Trim any excess dough and repair any tears or cracks using the trimmings. Cover loosely with plastic wrap and chill for an additional 30 minutes.
Preheat the oven to 425°F.
Prick the crust all over with a fork. Weight the bottom, either with pie weights or a circle of foil topped with dried beans. Bake until very pale gold in color, 8 to 12 minutes. Allow to cool for 10 minutes.
Reduce the oven temperature to 325°F and open the door for a minute or two to be sure it cools down adequately.
Place the spinach inside a kitchen towel or double thickness of cheesecloth and wring out as much excess liquid as possible. Set aside.
Heat the butter in a small skillet over medium heat. Add the scallions and sauté until slightly softened, 2 minutes. Add the spinach, combine well and season to taste with salt and pepper. Remove from the heat and set aside to cool.
In a large mixing bowl, vigorously whisk together the eggs and half-and-half until pale yellow and frothy. Add 1/2 teaspoon salt and a few grinds of black pepper. Stir in the grated cheese and cooled spinach, then carefully pour the entire mixture into the prepared crust.
Bake for 30 to 40 minutes, or until a knife inserted in the center comes out clean. Allow to rest for at least 5 minutes before cutting.
Tips for Making This Recipe
You can replace the spinach and scallions in this recipe with up to 1-2/3 cups of a different vegetable, meat or combination of the two. Just be sure that whatever you add is chopped small and thoroughly drained of any excess liquid.You can also vary the cheeses depending on your other ingredient choices.Here are some suggestions: