Preheat the oven to 400 degrees F.
In a saute pan, heat the olive oil. When the oil is hot, add the onions, celery, and peppers. Season with salt and cayenne. Saute for 2 minutes, or until the vegetables are wilted. Add the garlic, shrimp, and stock. Season with salt and cayenne. Cook for 2 minutes and remove from the heat. Turn the mixture into a bowl. Stir in the bread crumbs. Add the parsley and reseason if needed. Set stuffing aside to cool.
Place the flounder, brown side up, on a cutting board in front of you. Using a sharp boning knife, cut along the center bone of the fish. Carefully "peel" open the fish, folding the flesh back to open up a cavity in the fish. Work your way around the bones. You want to remove the whole skeleton of bones, leaving you with one piece of fish, all opened up. Season the fish with Essence. Fill the cavity with the cooled stuffing. Fold the flaps over the stuffing. Repeat the process for the other fish. Place the fish on a parchment-lined baking sheet. Drizzle the fish with the butter. Place the pan in the oven and bake the fish for 20 to 25 minutes. Remove the fish from the oven and serve.
Combine all ingredients thoroughly and store in an airtight jar or container.
Recipe from "New New Orleans Cooking", by Emeril Lagasse and Jessie Tirsch. Published by William Morrow, 1993.