Make a filling by mixing the yoghurt with the baking powder. To them, add the eggs and crumbled feta cheese. Mix well. It all depends on the size of the eggs but don't worry if the filling looks a little runny.
Lay out the Phyllo Pastry sheets. Pour a little oil onto each (about 1 tbsp).
Smear the oil all over the sheet, using a brush to help you. Fold the oiled sheet and place stuffing on each - 1 1/2 tbsp of it and spread out along the sheet.
Fold them again and form triangular, rectangular or whatever shapes you like. Once prepared, arrange them in a tray, covered with baking paper.
Put a small piece of butter on top of each Phyllo Pastry, pour 1 tbsp water or sparkling water on top of each.
Put them in a preheated 356°F (180 °C) oven and bake until ready - to a nice crisp.