2 sheets puff pastry (defrosted, if frozen)
1 kg fresh baby spinach, or 500g frozen spinach, defrosted.
2 scallions
2 Tbsp. dill
75g Greek feta, crumbled
1 lemon
1 tsp. kosher salt, plus more
freshly ground black pepper, plus more
All-purpose flour (for rolling)
1 large egg
Wilt spinach in a frying pan over a little bit of olive oil. Let cool. If using frozen spinach, place in a colander to drain.
While spinach cools, finely chop 2 scallions and transfer to a medium bowl. Finely chop 2 Tbsp. dill and add to bowl. Crumble Greek feta into small pieces and add to bowl. Add zest of 1 lemon. Season with 1 tsp. kosher salt and freshly ground 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.
Find a round object that’s 10–12″ in diameter (the larger, the better – look for a large pan lid). 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. Transfer pastry round, still on parchment, to a baking sheet. Chill. Repeat with the second sheet of pastry.
Crack 1 large egg into a small bowl and beat 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 1/2″ border. Place second round of pastry on top 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 tart 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 400F/200C. Brush tart all over with reserved egg wash; season with salt and pepper. Bake tart until risen and well browned all over, 30–35 minutes.