Ideally, you’ve defrosted your 1 17.3-oz. package frozen puff pastry for at least 8 hours in the fridge. But if you haven’t, take the 2 rolled-up sheets out of the box and place on a parchment-lined baking sheet. Don’t unfold yet or they’ll crack. Set a timer for 10 minutes, flipping rolled-up sheets halfway through. If, after 10 minutes, they’re pliable enough, unfold, separate with a sheet of parchment, and chill. If not, wait another 5 minutes. Puff pastry goes from stiff to flabby and sticky in a matter of minutes, so you want to be careful.Cut one slit in 2 10-oz. packages frozen spinach. Place both packages on a large, microwave-safe plate, then microwave until thawed, 8–10 minutes. (If you remembered to thaw your spinach in the fridge, you can skip the microwaving step.) Open packages carefully and drain in a fine-mesh sieve. Set aside until cool enough to handle. While spinach cools, finely chop 2 scallions and transfer to a medium bowl. Finely chop 2 Tbsp. dill and add to bowl. Crumble 2½ oz. Greek feta in brine into small pieces (no bigger than dried chickpeas) and add to bowl. Grate in 2 garlic cloves and zest of 1 lemon. Season with 1 tsp. kosher salt and ¼ tsp. black pepper.

While spinach cools, finely chop 2 scallions and transfer to a medium bowl. Finely chop 2 Tbsp. dill and add to bowl. Crumble 2½ oz. Greek feta in brine into small pieces (no bigger than dried chickpeas) and add to bowl. Grate in 2 garlic cloves and zest of 1 lemon. Season with 1 tsp. kosher salt and ¼ tsp. black pepper.


Transfer spinach to a dish towel and squeeze over the sink—you want to get rid of excess moisture that'll make your pastry soggy. You’ll be surprised by how little spinach is left, but that’s okay. Chop and add to bowl with scallion mixture.





Stir to combine, making sure to break up any spinach clumps. (You should have 2½ cups spinach mixture, in case you’re measuring.)


 Time to assemble! Find a round object that’s 10–12" in diameter (the larger, the better). We used the lid of a large Dutch oven, which is 11". Place one of the pastry sheets, still on parchment, on a work surface or large cutting board. Dust lightly with flour, both over and under. Roll it out, rotating parchment 90° (so you’re rolling in all directions) and dusting with flour if pastry sticks, until it’s at least 1–2" larger than your round object.


 Place round object over pastry, press to indent, then use a sharp knife to trace the circle. Set aside the excess pastry (save it for now; if your pastry tears, you can use a scrap to patch it up!). Transfer pastry round, still on parchment, to a baking sheet. Chill while you repeat with the second sheet of pastry.




Crack 1 large egg into a small bowl and beat to combine with a fork. Brush egg wash all along circumference of one pastry round (this will seal the two pieces of pastry together); reserve remaining egg wash for later. Spread spinach mixture over, leaving a ½" border. Place second round of pastry on top (if you’re having trouble moving it, fold it into quarters, then unfold on top of the spinach) and press gently to seal. Using a small cup or shot glass (2" in diameter), make an indent in the very center. Your pastry might be slightly warm by now. If so, chill 10–20 minutes.
 






Once pastry is cool, transfer the whole set-up, parchment and all, to a work surface. With a chef’s knife, cut pastry into 4 quadrants, stopping when you reach the center circle. Cut each quadrant in half, then in half again, so that you have 16 spokes. Transfer tarte with parchment back to sheet tray. (We’re doing this so that you can make sharp cuts and avoid transferring a delicate item.)




Working with one spoke at a time, pull gently away from the center (to extend the length of each piece), then twist to expose the spinach insides. Aim for three or four twists. Nudge them around to distribute evenly. Freeze until cold, 10–15 minutes.




Meanwhile, place a rack in middle of oven; preheat to 400°. Brush tarte all over with reserved egg wash; season with salt and pepper. Bake tarte until risen and well browned all over, 30–35 minutes.