Pre-heat the oven to 200°C, 400°F, Gas Mark 6. Meanwhile, mix the sachet contents into the milk. Pour into a saucepan and bring the mixture up to the boil. Add the butter and stir until melted.
Add the turkey and mushrooms and stir well. Remove from the heat. Roll out the pastry and cut into four equal squares. Spoon the turkey mixture over the centre of each square.
Brush two pastry edges with a little egg and then bring the four edges together and seal well. Lift onto a baking sheet. Repeat with the remaining three pastry squares. Brush the surfaces with the remaining beaten egg and bake for 20 minutes. Serve with roasted peppers and steamed peas.
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