Two days before serving, boil potatoes whole, with skins, until tender, about 25 minutes. When you can insert a fork and remove it easily, they are done.
Drain, and refrigerate.
The day before serving, peel and grate the potatoes. I like to use a food processor with grating attachment.
Place the potatoes into a large bowl and toss gently with melted butter, half-and-half, onion, salt and pepper. Cover and refrigerate.
The day of the meal, preheat the oven to 350 degrees F (175 degrees C).
Bake for 1 hour, uncovered. You may broil for a minute at the end to brown the top if you like.
