Preheat the oven to 190°C / 375°F / Gas Mark 5.
Peal, core and halve the apples.
In a metal saucepan warm the butter, add the brown sugar and melt. Place the apples into the pan with the flat side facing upwards.
Cover the apples with a sheet of puff pastry, tucking the edges under the apples.
Egg wash the pastry before baking in the oven for 15 minutes.