Spread out the phyllo pastry sheets, with the shorter side facing you. Crumble the feta cheese (if possible, use homemade). Beat 2 eggs and 1 egg white with a pinch of salt with a fork.
Put the egg yolk in a bowl and add 1 tablespoon oil to it, beat it as well. You're going to use it later for smearing the ready phyllo pastries.
Add the yoghurt to the egg mixture. Put the baking powder in 1 tablespoon flour and stir. Add these to the egg and yoghurt and stir once again.
Use a spoon to distribute the mixture onto 2 phyllo pastry sheets. Distribute it over the entire sheet. Sprinkle feta cheese on top. Fold both ends inward about a finger wide and then wrap it into a roll. This is done to make large and long phyllo pastries and prevent the filling from leaking out.
Place the roll in an oven dish laid out with baking paper. Repeat this process with another 2 of the sheets. Roll up the 2 large and long phyllo pastries. Smear them with the yolk mixture and sprinkle with sesame.
Cut the butter into small pieces. Distribute them on top of the phyllo pastries. Take another 2 sheets, distribute the egg, flour, baking powder, yoghurt mixture on them. Sprinkle with the feta. Fold it in 2, going from left to right to produce a long, half sheet. Take the left end and fold it at an angle toward the right to obtain a triangle. Do this for the final 2 sheets.
What you end up with is 2 long phyllo pastries and 2 large triangular ones. Smear the triangular ones with egg yolk mixture and sprinkle with sesame seeds as well. Distribute small pieces of butter on top. Bake in a preheated 356°F (180°C) oven until ready. They need to bake well.