Preheat oven to 200C. Lightly grease a baking tray. In a small bowl, mix the egg and milk until just combined. Put the egg wash to one side.
Heat a frypan on low-medium heat. Add spinach and dry cook for 1-2 minutes until just wilted. Take off heat. Cool a little and squeeze out the excess juice. In a bowl, mix the cooked spinach, ricotta, cheddar and chives then put to one side. Take your sheet of pastry and cut into quarters. Then spoon spinach and cheese mix onto half of each quarter of pastry. Fold the unfilled half of pastry over the top of the filling, forming a triangle. Press then ends closed on all three sides with a fork then place onto prepared baking tray. Brush with the prepared egg wash then bake for 20 minutes or until golden. Serve warm with salad or vegetables.
Reheat any leftovers in the oven for 5 minutes on 180C. Freeze any uncooked triangles for up to 1 month.