We preferred the brightness and intensity of fresh horseradish in this sauce, but prepared horseradish worked well, too. If you use bottled, reduce the vinegar to 1 tablespoon. Look for fresh horseradish root in the produce section, often near the fresh ginger. Peel and finely grate the root with a wand-style grater. If you have extra horseradish, try grating it into mashed potatoes, or over a warm steak or pork chop.