3 baking potatoes, peeled and cut into 1-inch chunks
1 1/2 teaspoon salt
1/4 cup milk or half-and-half
1 cup sour cream
1 1/2 cups grated cheddar cheese
1 bunch scallions, chopped (about 1 cup)
1/2 teaspoon black pepper
Preheat oven to 375.
In a medium saucepan over medium-high heat, combine the potatoes and 1 teaspoon of the salt and cover with water.
Bring to a boil and cook until tender, about 20 minutes. Drain, place in the bowl of an electric mixer, and mix just until fluffy. Do not over-mix. Add the milk or half-and-half, sour cream, 1 cup of the cheese, the scallions, the remaining 1/2 teaspoon salt, and the pepper and mix well.
Transfer the mixture to a 2 1/2 quart baking dish and sprinkle with the remaining cheese.
At this point you can wrap the dish and refrigerate for up to one day before baking.
Bake for 30 to 40 minutes (45 to 55 minutes if the dish was refrigerated), until browned and bubbling on top. Serve warm.