Slice a generous pint of cold boiled potatoes. Put into the brightest of saucepans butter the size of a pigeon’s egg, and when it bubbles add an even tea-spoonful of flour (the sauce not to be thick), which cook a moment, and then pour in a cupful of milk (or, better, cream), salt, and pepper; stir with an egg-whisk until it boils, then mix in the potato-slices. When they are thoroughly hot they are ready to be served.