Chicken, red pepper and brie puff pie

1. Cut each chicken breast almost in half lengthways and open out to form a large flat fillet. Put each fillet between plastic film and bat out with a rolling pin to flatten. Put in a shallow dish and sprinkle over the lemon zest, juice, salt, pepper, thyme leaves and oil. You can now cook the chicken straight away or leave the fillets to marinate for up to a day covered with plastic film.
2. Heat a large non-stick frying pan or a griddle pan until really hot. Fry the chicken (you will need to do this in batches), turning often, for about 8-10 minutes until browned and just cooked. Remove and leave to cook.
3. Drain the peppers, cut in half and pat dry on kitchen paper. Slice the brie. Roll out the pastry to a 35cm/14in square. Arrange three chicken fillets along the centre third almost to the edges. Cover with half the peppers, then all the brie, followed by the rest of the peppers and finally the remaining chicken fillets, seasoning between the layers as you go.
4. Brush the pastry with beaten egg. Draw up the two long edges over the filling and pinch together following the shape of the filling. Seal the ends, then trim off the excess pastry with scissors or a knife. Pinch the pastry join all along between your fingers, like you would a pasty.
5. Carefully transfer the pie to a damp baking sheet. Brush liberally with egg and sprinkle with parmesan. The pie can now be chilled for up to 24 hours.
6. Preheat the oven to 200C/400F/Gas 6 from cold. Bake for 30-35 minutes until the pastry is crisp and golden. Cool for 5 minutes, then transfer to a serving plate and cut into thick slices to serve.