Preheat oven to 180°C.
Melt butter over medium high heat in a saucepot.
Add flour and cook for a minute.
Add milk in a thin stream while stirring, to avoid lumps. Cook for 3-4 minutes.
Stir in chicken pieces and wilted swiss chard. Remove from heat and stir in cheese.
Remove mixture from pot and allow to cool.
Roll out pastry on a floured surface to 4mm thick.
Cut pastry into 9cm squares, place a spoon of filling on one corner leaving a border.
Brush the edges of pastry with egg, fold closed and glaze with remaining egg.
Bake for 15-20 minutes until golden.
Cool on a wire rack before storing in an airtight container in the fridge.