Fillet Schmaltz herrings and soak in water overnight. Combine all ingredients for marinade and boil for 5 minutes. Let cool.
Place fillets in a crock and pour cold marinade over them. Marinate for 4 to 5 days.
Remove herring fillets from marinade and cut into one-inch pieces. Drain well and mix with mustard sauce. Garnish serving dish with fresh dill and pimentos.
To make mustard sauce, combine wine, shallots, and mustard seeds and heat to boiling. Reduce liquid by three-quarters and cool. When cool, mix into mayonnaise. Add mustard; after 5 to 10 minutes, strain through cheesecloth.