Preheat oven to 400�F. Place the potato strips in cold water to keep them from discoloring. Heat 2 tablespoons of butter and 2 tablespoons of oil in a 10-12 inch skillet; when the foam subsides, add the onions and cook 10 minutes, stirring frequently, until they are soft but not brown. With a pastry brush or paper towels, spread a 1.5 to 2 litre souffl� or baking dish with the remaining half tablespoon of butter. Drain the potatoes and pat them dry with paper towels. Arrange a layer of potatoes on the bottom of the dish and then alternate layers of onions and anchovies ending with potatoes. Sprinkle each layer with a little white pepper. Scatter bread crumbs over the top layer of potatoes and dot the casserole with the 2 tablespoons of butter cut into bits. In a small saucepan, heat the milk and cream until it barely simmers, then pour over potatoes. Bake in the center of the oven for 45 minutes or until the potatoes are tender when pierced with the tip of a sharp knife or skewer and the liquid is nearly absorbed.