½ cup whole-wheat flour
½ tsp lukewarm water
⅔ cup active dry yeast
¼ cup plus 2 tablespoon extra-virgin olive oil
1 medium onion, diced
1 Tbsp ground sumac, see Note
2 tsp fresh lemon juice
freshly ground pepper
2 10-ounce packages frozen spinach, thawed and squeezed dry
1 large egg, beaten
1. In the bowl of a standing electric mixer fitted with the dough hook, combine the 1 cup plus 2 tablespoons of all-purpose flour with the whole wheat flour, yeast, water, 1/2 teaspoon of salt and 3 tablespoons of the olive oil. Mix at medium speed until a soft, supple dough forms, about 10 minutes. Using oiled hands, transfer the dough to an oiled bowl. Cover with plastic wrap and let the dough stand in a draft-free spot until slightly risen, about 1 hour.
2. Meanwhile, in a large skillet, heat the remaining 3 tablespoons of olive oil. Add the diced onion and cook over moderate heat until softened, about 7 minutes. Add the sumac and lemon juice and season with salt and pepper. Stir in the spinach and let cool completely.
3. Preheat the oven to 450° and line 2 baking sheets with parchment paper. Divide the dough into 10 pieces. Form each piece of dough into a ball, dust with flour and let stand for 10 minutes.
4. On a lightly floured surface, roll each ball of dough to a 5-inch round. Spread the spinach filling over half of each round, leaving a 1/2-inch border. Brush the rims with water and fold the dough over to enclose the filling; pinch the edges to seal.
5. Transfer the spinach pies to the prepared baking sheets and brush the tops with the beaten egg. Bake the pies for about 18 minutes, or until golden; shift the pans from top to bottom and front to back halfway through baking. Transfer the spinach pies to a platter and serve warm or at room temperature.