Place the potatoes in a large saucepan.

Cover with water and bring to a boil.

Let boil until tender, 25 to 30 minutes.

Drain the potatoes.

When cool enough to handle, dice with the skin on.

In a large bowl, stir together the milk, mayonnaise, and horseradish.

Add the potatoes, celery, pickles, and scallions.

Toss gently until everything is covered with mayonnaise.

Sprinkle with salt and pepper to taste.

Cover and chill before serving.