In a large bowl, combine the halibut, bread crumbs, Essence, salt, cayenne, green onions, parsley, dill, mayonnaise, and egg. Fold with a rubber spatula, gently mixing in the halibut and bread crumbs. Shape the mixture into 4 (3/4-inch) thick patties and place on a plate. Refrigerate for 20 minutes.
In a large skillet, melt the butter over medium-low heat. Add the cakes and cook until golden, 3 to 5 minutes per side. Remove from the heat. Garnish 4 salad plates with watercress.
Place 2 cakes on each plate and top with a dollop of tartar sauce. Garnish with chopped parsley and Essence, and serve.
Yield: 8 halibut cakes