Preheat the oven to 180°C

Heat the oil in a large deep sided pan over a medium heat. Once hot, add the leek and bacon, and cook for 4 minutes or until the leek has softened

Add the chicken, mushrooms and garlic. Stir for 5-8 minutes or until the chicken becomes golden. Reduce the heat to low and stir through the herbs, ricotta, milk, parmesan and lemon. Season with salt and pepper (and add extra milk if the mixture is dry)

Transfer the mixture to a baking dish and cover with the pastry. Use a fork to gently press the pastry into the edges of the dish to create a seal. Trim any excess and then lightly brush the pastry with the egg. Use a knife to pierce the pastry in the centre, and then place into the oven to bake for 30-40 minutes or until puffed and golden

Remove from the oven and set aside for 5 minutes before serving