Coarsely grate the rind from each lemon and juice all of them. Add sugar, horseradish, powdered mustard, turmeric, cloves, allspice, white pepper, finely minced onion, and cayenne pepper. Mix well and let stand, covered, overnight in a nonreactive container such as plastic, glass, or stainless steel.
The next day, bring to a boil and cook slowly, uncovered, for