Put all ingredients except leaf tea and sumac in a large pot, add 2 quarts water and bring to a boil. Simmer for about 20–30 minutes. Take out 1 quart and pour into a separate saucepan. Add mulberry leaf tea and sumac and season liquid to taste. This is your poaching liquid.

Leave the remaining liquid in the pot to continue to simmer for another 30 minutes (going longer can cause the bones to start to dissolve and make the sauce chalky). This liquid is the basis for a reduction to pour over the fish when serving. To finish, strain the liquid through a fine-mesh sieve into a smaller saucepan. Reduce the liquid until desired thickness and flavor is reached. Add salt to the final sauce as desired. Be careful not to over-season the poaching liquid or stock prior to reducing, because as it reduces it may become too salty.

To poach the fish: Bring the poaching liquid almost to a boil. Lower the thinly sliced fillets into the liquid to poach for about 30 seconds to a minute, depending on thickness (the fish turns opaque and flakes easily with a fork when it is done). Serve immediately: Divide the poached fish over 4 plates, pour reduction on top. Finish the dish with a touch of sumac finishing salt to add brightness and acidity to the dish.