Process chopped horseradish root to fine shavings, in a food processor.

Add enough vinegar in a steady stream, with processor running, to form a spreadable paste. You may not need all of it. Transfer sauce to a bowl.

Stir in sugar and salt. Refrigerate in a jar with a tight lid. After a half hour the flavor is well balanced.

To cook the potatoes, place them in a 6–8 qt. stockpot. Add cold water to cover the potatoes by 1–2". Bring to a boil over medium-high heat. Reduce heat and simmer potatoes 15–20 min., or until they can be broken easily with a fork. Don’t overcook or they’ll absorb too much water.

Simmer milk and butter in a saucepan. Drain potatoes and return them to the pot. Over med. heat, briefly cook the potatoes to dry, stirring constantly. Fill ricer with some potatoes and push them through the ricer into a bowl. Repeat in batches with remaining potatoes. Gradually add the warm milk and butter to the potatoes, stirring to combine.

Stir in Horseradish Sauce and season with salt to taste.

	Cut peeled potatoes into 1 1/2" chunks so that they will all have the same cook time.