Step 1

Cover lox with water, and soak in refrigerator 8 hours, changing water once.

Step 2

Cut lox into 1-inch cubes (you should have about 6 cups). Place in a large glass bowl, layering with onions.

Step 3

Stir together 5 cups water, the vinegar, and sugar until sugar dissolves. Add seeds, allspice, bay leaves, and red-pepper flakes, then pour over lox. Cover with plastic wrap, and marinate 4 hours at room temperature. Transfer to refrigerator, and marinate at least 48 hours and up to 1 week. Serve with sour cream sauce.