In a bowl, dissolve the yeast in the lukewarm water. Once the yeast has been dissolved add in the milk, oil, sugar, salt and egg white and stir until well mixed. Add in the flour and butter and mix to a dough. Put the dough into a greased bowl and cover with cling film or a tea towel and set in a warm area. Let is rise until doubled in size, about 1 hour.
Preheat the oven to 180 C / Gas 4. Line a baking tray with baking parchment.
Grab egg sized pieces and make flat with your hands (in to a circle). Put the filling (whatever you want, I normally do crumbled feta cheese and parsley) on one half of the circle then cover the filling with the other half of the dough and gently seal the edges, like a half moon. Place on the prepared baking tray. Brush with lightly beaten egg and sprinkle with sesame seeds.
Bake in the preheated oven for 40 minutes or until risen and golden brown. Remove from the oven and serve warm, or transfer to a cooling rack to cool completely.