- Preheat the oven to 475 degrees (225 degrees C).
- Place a layer of sliced potatoes onto the bottom of a large baking dish. Top the potatoes with a layer of sliced onions, and then a layer of anchovy fillets. Repeat layers up to the top of the dish, ending with a layer of potatoes on top. Drizzle about 2/3 of the cream over the dish, and the reserved liquid from the anchovies. Sprinkle the breadcrumbs over the top, and dot with pieces of butter.
- Bake for 30 minutes on the middle rack of the oven. Add the remaining cream, and continue baking for another 15 minutes, or until the potatoes are tender.