Preheat your oven to 400°F.
Add the softened cream cheese, thawed and drained spinach (see Note 1 below), feta, Mediterranean herb feta, queso fresco, dill, garlic powder, onion powder, and salt to a medium mixing bowl. Stir using a spoon or spatula, making sure all ingredients are well combined. Set aside.
8 oz cream cheese, 10 oz frozen spinach, 1 cup crumbled feta, 1 cup crumbled queso fresco, ¼ cup crumbled Mediterranean herb feta, 1½ tsp dried dill, ⅛ tsp garlic powder, ⅛ tsp onion powder, ⅛ tsp salt
On a lightly-floured surface, use a floured rolling pin to roll out the puff pastry into a large (10" x 10") square. Cut this large square into four smaller squares—about 5"x5" each. Repeat the same process with the second puff pastry sheet.
1 box puff pastry (2 sheets)
Use a fork to dock, or poke small holes into, the middle of each puff pastry square. Leave about a ½-¾" undocked border around the edge. Add about 2 heaping tablespoons of filling to each puff pastry square, spreading it into a diagonal across the docked portion of the dough (so the filling will peek out when two opposite corners are pinched together).
Whisk together the egg white and water in a small bowl. Using a pastry brush, dab some of the egg wash onto the corner of the puff pastry square that will be folded in last—this will act as glue to hold the two corners together. Fold in the opposite corner, then the corner that has been brushed with egg wash. Pinch/press the two corners together to secure them. Brush the outside and edges of each pastry with more egg wash.
1 egg white, 1 tsp water
Bake 4 pastries at a time on a half sheet pan covered with a silicone baking mat (or parchment) for 18-20 minutes at 400°F, turning the pan 180° halfway through to ensure even baking. The pastry should be puffy and golden brown and the filling should be cooked but not dried out when the pastries are done baking.
Remove the spinach and feta pastries from the oven and move them to a wire cooling rack using a spatula. Once they have cooled slightly, enjoy the pastries! Store any leftovers in an airtight bag or container in the fridge. See my notes in the post content above for tips on reheating these pastries.