How to Make It
To make the dough, whisk together the flour and salt, then add the butter and rub in with your fingers, a pastry blender, or 2 butter knives. You’re looking for pieces of butter about the size of a kidney bean. The most important thing about making pie dough is keeping everything cold . You don’t want the butter to melt before it gets into the oven, because it’s butter steam that makes pie dough crisp and flaky. If the butter starts to feel soft at all, transfer the whole bowl to the fridge.
Pour the water (strained over ice) over the flour and gently but authoritatively combine with your hands. The dough should just come together. If it doesn’t (this may be especially true if you’ve added whole wheat flour), add a bit more cold water, tablespoon by tablespoon, until it does. Split the dough into two discs, wrap each in plastic, and stash in the fridge for at least half an hour, or pop in the freezer for a rainy day up to a month down the line.
While the dough chills, make the filling. Strip the leaves of the greens from their stems, reserving tender stems and discarding woody or dense ones. Roughly tear large leaves like those of kale or chard or roll a stack of the leaves into a cigar and slice into inch-thick ribbons. Wash and finely chop the stems and set aside; wash the greens very well and dry them. They do not have to be perfectly dry, but they should be very clean, otherwise you will discover that you’ve made sand and grit pie instead of greens and cheese pie.
In your largest frying pan, combine the olive oil, garlic, red pepper flakes, and cumin seeds. Pile the greens on top; it will seem like a lot of greens, but they’ll shrink down as they wilt. Pour the water over the greens, season with a good pinch of salt, turn the heat to medium-high, and cover with a lid or a piece of aluminum foil. Stir the greens occasionally (I like a pair of tongs for this job) until they are completely wilted. Transfer the greens to a strainer to cool to room temperature. When they have, squeeze the moisture from them and transfer to a bowl.
Season the greens with the red wine vinegar and additional salt and pepper to taste (keep in mind that you’ll be adding a salty cheese in a moment, so be conservative with the salt), plus a bit of honey if you’ve used a bitter green like dandelion. Stir well to combine, then crumble in the cheese and stir again. Taste. This is your last chance to make sure everything is seasoned correctly. When it’s where you want it, add the 2 eggs and stir once more. Set aside.
Line a baking sheet with parchment paper. On a lightly floured surface, roll one disc of the pie dough (leaving the other disc in the fridge) into a large rectangle about 10 inches by 16 inches. Carefully transfer this piece to the parchment paper (I like to fold the dough over my rolling pin and transfer it that way). Distribute the greens over the dough, leaving about 1½ inches of room on all sides. Put the entire thing into the refrigerator while you roll the second disc of pie dough out. Set this piece over the top of the pie, lining up the edges as best you can.
Trim the edges of the dough to tidy it, leaving about an inch and a half on all sides. Now it’s time to crimp: First, fold the edges of the dough beneath the pie. Use a fork to firmly tamp down the edges, or “flute” it by making a “C” shape with the thumb and forefinger of one hand, positioning it on one side of the dough, and using the forefinger of your other hand to press the dough into the mouth of the “C” shape to form a point (or a curvy point). Do this all the way around the edges of the pie.
Use a sharp knife to cut a few slits into the top crust, then put the sheet tray right into the freezer. Leave it there while you preheat your oven to 400°F.
Brush the crust with the egg beaten with water or a few tablespoons of milk (you can use a pastry brush or your fingers). Bake the pie until deeply golden brown and crisp-feeling when you tap it lightly, 45 to 60 minutes. Let cool slightly before you cut into it.