For the filling,
Combine the cherries with the apples, sugar and vanilla essence in a baking dish and cover with foil. Bake at the 180°C/ gas 6 for 20 minutes. Remove from the oven and drain off the juice into a saucepan. Leave the fruit to one side to cool.
Mix the cornflour with 3 tbsp of the juice, then stir back into the juice in the pan. Bring the juice to a simmer, then cook until it thickens. Cool. Add the fruit to the pie base and pour over the thickened juice.
Butter a tart pan (or pie dish) and set aside.
Roll out the pastry to a nice thin size and line the tart pan.
Trim off the extra dough and roll it out into a square.
Cut the trimmed or extra pastry into thin strips (half inch) and use them to top the pie in a criss-cross fashion.
Use a beaten egg to brush over the pastry. Sprinkle with brown sugar.
Bake for 45 minutes at 190˚ C.
Serve with a generous dollop of ice-cream or cream.