Mix flour and salt, then rub in chilled butter and add 150-180ml cold water to form dough.
Roll dough into a rectangle and grate 60g frozen butter over bottom two thirds.
Fold dough like a letter, rotate 90 degrees, and repeat with remaining frozen butter.
Rest the pastry in the fridge for 30 minutes.
Sauté leeks with orange juice, zest, and sherry until liquid is reduced to a few spoonfuls.
Stir in flour, then gradually add stock and simmer for 5 minutes until thickened.
Mix in mustard, turkey, ham, tarragon, and cream, then season and allow to cool in a dish.
Preheat your oven to 200°C.
Roll pastry to 5mm thick and attach a 2cm strip to the rim of the dish using egg wash.
Place the pastry lid over the dish, seal the edges, and brush the top with egg wash.
Bake for 35-40 minutes until the pastry is risen and golden-brown.