Melt the goose fat. Slice the bread into 7-10mm slices, remove the crusts then brush liberally with the melted goose fat. Use to line individual pie or cocotte moulds - cut discs to fit the bottom and tops and then each slice into three strips to cover the sides. Make sure that all the bread pieces are overlapping and that there are no gaps.
Bring the stock to a simmer, slice the leeks into 1cm rounds and poach in the stock until tender. Mix the butter and flour together to make a paste, gradually add this to the stock whisking as you go. Simmer until the stock is thickened and raw flour taste is cooked out. Add the cream and return to the boil. Turn off the heat and add the chervil, turkey and ham.
Divide the mixture between the moulds then top with the remaining bread discs. Cover the top with foil and bake for 20-25 minutes - remove foil for the last 5 minutes.
Allow to rest for 10 minutes before turning out and serving.
Ideally serve with some savoy cabbage dressed with wholegrain mustard.