Combine all stuffing ingredients and correct seasoning. The stuffing must taste delicious by itself. This stuffing should be made at time of final preparation or the bread stuffing will have a heavier consistency than desired.
Preheat oven to 400 degrees F. Keep fumet hot in a pot on the stove.
Check the entire fish for scales or bones. This is done by running your fingers over all surfaces of the fish. Remove any bones with a pair of needle-nosed pliers.
Place fish on a lightly oiled sheet of aluminum foil in large pan. Salt with kosher salt inside and out.
Since there are crevices within the fish, use your hands to place the salt throughout. Pepper the inside and outside of the fish. Lightly place a coat of olive oil on outside of fish. Stuff fish with bread mixture. If the mixture does not adequately remain in the fish cavity, gently tie the fish around with butchers twine every few inches. Place fish in oven and pour 3 cups of the hot fumet over fish. Cover and cook for about 80 to 90 minutes, basting with hot fumet every 15 minutes.
To check for doneness use a fork in the thickest part of the flesh and determine that the meat is opaque, signifying doneness. The fish will have an internal temperature of 130 degrees when it is done.
Remove fish from the pan with foil. Gently peel back foil and place fish on a platter. Slice and serve.
Simmer first 9 ingredients for 25 to 30 minutes. Add fish parts. Simmer for 1 hour, covered. Salt and pepper, to taste.
Strain through chinois. Strain again, using cheesecloth. Place liquid in tightly covered container and refrigerate until needed.