Baked Haddock With Mustard-Tarragon Marinade Substitutes: Boston Blue, Hake 2 tbs. rice vinegar or white wine vinegar 2 tbs. olive oil 1 tbs. dijon mustard 1/2 tsp. dry tarragon leaves or 1/2 tbs. chopped fresh tarragon leaves 1/8 tsp. pepper 1-1 1/2 lbs. haddock fillets In a large bowl whisk the vinegar, oil, mustard, tarragon and pepper. Rinse fish and pat dry. Add the fish to the marinade and ...