2 pounds russet potatoes (about 4 medium), peeled and cut into 1-inch pieces
1 teaspoon kosher salt, plus more to taste
3/4 cup whole milk
1/4 cup unsalted butter
4 teaspoons prepared horseradish (not beet colored)
Freshly ground black pepper
The potency of prepared horseradish can vary greatly, so adjust the quantity to taste, if needed.