Soften the butter to room temperature. Mix together the flour and the pastry and then add the egg yolk, a pinch of salt and then water. Mix well but be careful not to overwork the pastry. Roll out into a disc and chill in the fridge for 1 hour.
Preheat the oven to 200°C. Butter a 10 inch quiche dish.
Roll out the pastry to 3mm thick and a circle 4cm bigger than your quiche dish. Press the pastry into your buttered quiche dish. Cover with a sheet of baking parchment and then cover with baking beans. Blind bake the pastry for 20 minutes. Remove the pastry base from the oven and lower the oven temperature to 180°C.
Peel and finely slice the leeks then rinse in cold water. Melt the butter in a frying pan and add the leeks. Cook over a low heat for 10 minutes, making sure that the leeks do not burn then add another knob of butter. Season with salt and pepper.
Mix together the cream, whole eggs and the egg yolks. Season with salt, pepper and nutmeg.
Place the leeks on to the cooked pastry base, sprinkle with gruyere or emmental cheese and then pour in the cream and egg mixture. Cook for 25 minutes at 180°C.
Remove from the oven and allow to rest for a few minutes before serving.
«Feel free to use ready made pastry but make sure to blind bake before adding the filling.»