Ready-made horseradish can be bought in any supermarket, but when fresh horseradish root is available in early spring, prepare it yourself -- the fresher the root, the sharper the bite.
Chop the horseradish root into 1/2-inch pieces. Place in the bowl of a food processor with vinegar, salt, and sugar.
Puree until finely minced and well combined, about 1 minute. Transfer to an airtight container, and refrigerate. Prepared horseradish will keep up to 2 weeks.
Horseradish root is sold in most supermarkets.