Preheat the oven to 180°C.
Divide the pastry in half; roll one half into a large round of pastry roughly ½cm thick. Use to cut 4 rounds of pastry roughly 12cm in diameter and use to line 10cm individual pie dishes. Press in well in the base and sides, then chill.
Melt the butter in a medium, heavy-based saucepan over a medium heat. Whisk in the flour to create a smooth roux, cooking gently, whisking occasionally for 2 minutes. Slowly whisk in the milk in a slow, steady stream until you have a thickened sauce. Simmer for 3-4 minutes, then add the diced turkey, carrot and the peas. Simmer for a further 3-4 minutes, then remove and adjust the seasoning.
Roll the other half of pastry out into a large round on a lightly floured work surface, roughly ½cm in thickness. Use a 10cm plate as a guide to cut 4 rounds of pastry that will be the lids. Fill the pastry cases with the turkey and vegetable filling. Place the pastry lids on top and seal at the rim. Decorate the rim with the tines of a fork, then brush the tops lightly with the beaten egg.
Bake for 25-30 minutes until the pastry is cooked and golden brown in colour. Check the meat is cooked through with no pink showing. Remove and allow to cool before turning out.
Arrange on serving plates and garnish with the mixed lettuce leaves. Serve immediately.
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home and view the full Food safety at home video.