Split the vanilla pod and mix the vanilla seeds by hand with the sugar. Tip the vanilla sugar onto the butter and shake the pan until the sugar is evenly dispersed
Peel and core the apples and cut in halfway through the core. Pick out any pips. Arrange the apple skins side down. Pack the apples as tightly as possible
Cook on a baking sheet on the top of the stove until the apples have started to caramelise. You may need to change this tray a few times during the cooking process but it saves the oven top. This can take up to 40 mins
Roll out the puff pastry evenly to about 2mm thick on a floured surface and prick with a fork
Place on top of the apples and cut the excess pastry away. Egg wash and then bake in the oven at 200c/400f, gas mark 6 for approx 15 mins until pastry is brown
When cooked, press the tart with a plate that fits the inside of the pan and drain any excess liquid. Leave for 20 mins. Turn out onto plate and serve