Dough

Mix flour, baking powder, olive oil, vinegar, salt, and water and stir until a soft dough forms.  Let rest 20 minutes and knead again for a few minutes. 

 Divide dough into 10 portions; roll each portion into a ball. Place in container coated with oil and cover with plastic wrap to prevent dough balls from drying out let rest at least 5 hours. 

Filling

 Heat oil in a medium sauté pan over medium-high heat. Sauté onions and garlic for 5 minutes or until translucent. Transfer to a large bowl and add spinach and feta and stir to combine.

Prepare Borek

Line sheet pan with parchment and preheat oven to 375℉.

Take each ball on a greased board and flatten with your hands until paper-thin. 

On the bottom edge of the dough begin to spread out the filling from one end to the other.  Carefully roll the pastry up around the filling into one long log.  Then curl around into a spiral and place on prepared sheet pan. 

Brush the borek with egg, sprinkle with sesame seeds and bake for 25–30 minutes or until golden brown.