Pour the mineral water into a mixing bowl and add the salt and oil. Fold in the flour, adding enough to make a soft dough. Wrap the dough in cling film and chill it in the fridge for about 30 minutes. This makes it easier to roll out.
Preheat the oven to 180°C/350F/Gas 4. Take the dough out of the fridge and divide it into 4 balls. Roll out each ball as thinly as you can, then place a round chopping board or a plate underneath, letting the edges of the pastry overlap. This makes a kind of template for your filling.
Place a thin layer of filling over the pastry spreading it out as far as the edges of the plate or board underneath. Don’t overdo the filling – a little goes a long way.
Fold the edges of the pastry in towards the middle to form a nice pleated curly pie. Don’t worry if it looks a bit rustic – the folds make the curls in your curly pie. Repeat to make the remaining pies in the same way and place them on a baking tray.
Beat the eggs with the yoghurt and brush the mixture over the pies. Bake them for about 40 minutes until they are cooked through and have a lovely golden crust.
Serve with a salad.