MAKE THE TART: Preheat the oven to 400ºF. Line a baking sheet with parchment paper. To the bowl of a food processor fitted with the blade attachment, add the feta cheese and spinach and blend until smooth. Season with salt and pepper to taste, transfer to a bowl and set aside.
Place the artichoke hearts in the food processor and pulse until finely chopped. Set aside.
On a lightly floured surface, use a rolling pin to roll the puff pastry to a 12-by-12-inch square. Cut a circle that’s 12 inches across out of the puff pastry using a plate or mixing bowl of the same diameter. Place the round in the refrigerator and repeat with the second piece of puff pastry.
Place one round of puff pastry onto the prepared baking sheet. Spread the feta cheese mixture evenly over the puff pastry, leaving a 1-inch border around the edge.
Top with the chopped artichokes and raisins. In a small bowl, beat the egg and 1 tablespoon water until combined. Brush the egg wash around the edge of the puff pastry and place the second round of puff pastry on top, pressing the edges of the circle gently to seal.
Using a cup that’s with a 3-inch diameter, press gently in the center of the puff pastry round to make an indentation, without pressing all the way through. Cut the circle into quarters, then each quarter in half.
Cut each eighth into three pieces to make 24 strips total. Carefully twist the strips of puff pastry into a spiral without breaking the pieces off the center of the puff pastry. Repeat until all the strips have been twisted in the same direction.
Brush the tart with the egg wash and bake on the middle rack of the oven for 35 to 40 minutes, or until the puff pastry is golden brown.
MAKE THE GREMOLATA: Meanwhile, in a small bowl, combine the parsley, lemon juice and zest, olive oil and flaky salt. Mix to combine. Let sit to allow the flavors to marinate. Drizzle over the tart and serve immediately.