Peel potatoes and cut into French fries, about 1/4″ x 1/4″ x 2-3 inches long. Slice onion into half-moons
Butter a 2-3 quart baking dish. Layer the potatoes, onion, anchovies, salt and pepper in the dish, starting and ending with potatoes.
Then pour the double cream over and sprinkle the bread crumbs on top
Bake in the lower part of the oven for about 1hour or until the potatoes are soft and the gratin have a nice color If it gets to dark then just put on some foil but you know that