How to Make It
In a medium bowl, whisk the flour with the salt and make a well in the center. Add the olive oil and work it in with your fingers until the flour is evenly moistened. Add 1/3 cup of water and stir until a rough dough forms. Pinch the dough together; add another tablespoon of water if the dough seems too dry. Cover the dough with plastic wrap and let rest for 10 minutes.
Turn the dough out onto an unfloured work surface and knead until smooth, 5 minutes. Cut the dough into 6 pieces; cover with a moistened paper towel.
In a medium bowl, toss the onion with the sumac and a generous pinch each of salt and pepper. Add the spinach and stir in the pine nuts, lemon juice and olive oil. Season with salt and pepper.
Preheat the oven to 450°. Line a large baking sheet with parchment paper. On an unfloured work surface, roll out each piece of dough to a 6-inch round 1/8 inch thick. Spoon the spinach filling onto the center of each pastry round and fold into half-moons. Pinch the seams to seal and transfer the spinach pastries to the baking sheet. Bake for 18 minutes, or until golden. Serve warm or at room temperature.
Sumac is a fruity, tangy spice that is ground from the dried berries of a wild Mediterranean bush. It is available at Middle Eastern markets.