In a small bowl, combine ½ cup warm milk, sugar, and yeast. Allow the mixture to sit for about 5 minutes until foamy.
Transfer the yeast mixture to a stand mixer bowl. Add salt and half of the flour.
Mix on low speed while gradually adding the vegetable oil, remaining milk, and the rest of the flour.
Increase the speed and knead until a smooth, soft dough forms.
Shape the dough into a ball and place it in a lightly greased bowl. Cover and let rise in a warm place for 1 hour or until doubled in size.
Divide the dough into 18–24 equal portions and roll into small balls.
Cover and let rise for an additional 30 minutes.
Prepare the filling by chopping the spinach and placing it in a bowl. Sprinkle with salt and let sit for 10 minutes before squeezing out all excess moisture. If using frozen spinach, thaw completely and drain thoroughly.
Mix in the onion, tomato, olive oil, black pepper, seven spices, and sumac.
Add lemon juice immediately before filling the pastries.
Preheat the oven to 400°F (200°C) and line baking sheets with parchment paper.
Roll each dough ball into a 5-inch circle.
Place about 2 tablespoons of filling in the center.
Fold the dough into the traditional triangular shape and pinch the edges tightly.
Arrange the pastries on prepared baking sheets.
Brush each pastry with whisked egg.
Bake the Spinach Fatayer Recipe for 18–22 minutes or until golden brown.
Cool slightly before serving.