Creamy chicken, ham & leek pie

3 boneless, skinless chicken breasts, poached with a stock cube, 250 ml cooking liquid, 75 g butter, 2 slender leeks, trimmed and sliced, 2 garlic cloves, crushed, 50 g plain flour, 200 ml milk, 2-3 tbs white wine, 150 ml double cream, 150 g thickly carved ham, cut into 2 cm chunks, salt, peper, 1 shortcrust pastry

Melt 25 g of the butter in a large non-stick saucepan over a low heat. Stir in the leeks and fry gently for 2 mins, stirring occasionally until softened. Add the garlic and cook for 1 min more, then tip everything into a bowl.
Return the pan to the heat and add the remaining butter. Stir in the flour as soon as the butter has melted and cook for 30 secs, stirring constantly. Add the milk, a little at a time, stirring well. Gradually add the cooking liquid and the wine, then stir until the sauce is smooth and thick. Bring to a gentle simmer and cook for 3 minutes. While stirring season to taste, then remove from heat and stir in the cream.
Add the chicken, leeks and ham to the sauce and pour in a pie dish.
Roll the pastry out and cover the pie dish and trim off the excess. Using a sharp knife cut a small hole in the middle of the pasty (this allows the steam to escape while the pie cooks).
Preheat the oven to 220C. Beat the egg yolks and brush over the pastry. Place the pies in the oven and cook for about 45 minutes.