In large bowl, mix 1/2 c. Italian-style breadcrumbs, salt, celery seed, and cayenne pepper. Stir in egg, mayonnaise, mustard, lemon juice, horseradish, and onion. Stir well, and add crab. Stir gently until well-blended. Shape into 6 large patties.
Spread remaining 1/2 c. Italian breadcrumbs on plate. Prepare egg dip, and dip each patty first into egg and then into breadcrumbs, coating well. Cover prepared patties and refrigerate for at least one hour, no longer than overnight.
Melt 2 tbsp butter in frying pan and fry patties 4-5 minutes each side. Serve on onion rolls with tarter sauce and coleslaw, if desired.