Mix the egg and milk in a small bowl. Wash and dry the spinach leaves using spinner until they are completely dry well. Then chop them.
Put 2 tbsp olive oil to frying pan and add the chopped spinach pieces and chopped onions and stir them until they get soft.
Remove the spinach and onion mix from frying pan to a bowl and close the heat. Then add 1 tbsp olive oil to the frying pan and put 2 Phyllo pastry sheets on frying pan. Add the egg and milk mix on the phyllo sheets.
After adding egg and milk mix on top of phyllo sheet; put the spinach and onion mix and then add the feta cheese pieces on top of it.
Close the phyllo sheets from starting the corners and make sure it is closed well. Then open the stove heat to medium-low level and start to cook.
In every 10 minutes flip the Börek and make sure it has reach the gold crisp color.
Tip: Service it with Yogurt and Lemon slices.