Shred a whole cooked chicken (one of those deli ones works well) and use the carcass to make a stock. Fry off any veg you fancy adding (in this one we used carrot and leek). Make a roux and add the chicken stock. When thick, stir in some mustard seed and creme fraiche and simmer until thickened. Sttir in chicken and veg and stir into pie dish and top with puff pastry. Bake until golden.