ASSEMBLE THE BOEREK: Preheat the oven to 180 °C or 360 °F. Grease a backing dish (I used 30×20 cm or 12×8 inch rectangular dish) with a bit of olive oil. Lay a phyllo dough sheet in the middle of the baking dish, folding the ends inside and creating waves of dough. Smear with a bit of milk mixture. Spread half of the filling over the softened phyllo dough, cover with another layer of phyllo dough, fold the ends and smear with the milk mixture again, following by the rest of the spinach feta filling. Put the third and the last layer of phyllo dough on top of the filling, fold the edges and pour the rest of the milk mixture on top. Bake for 25-30 minutes. You’ll see that it’s ready when the top of the boerek is golden-brown, just like on the pictures. Enjoy!