Using a food processor, fitted with a metal blade, combine the egg, onions, green onions, celery, garlic, mustard, parsley and lemon juice. Puree until smooth. Season with salt and pepper. With the machine running and in a steady stream add the oil. Process until all of the oil is incorporated and the mixture is thick. Season with salt and pepper.
In a mixing bowl, toss the crabmeat with 1/2 of the Ravigote, reserving the other half for a later use. Season with salt and pepper.
Season the onion rings with a drizzle of olive oil, salt and pepper. Place the onions on the grill and cook for about 2 to 3 minutes on each side. Remove the onions and set aside.
In a large saute pan, over medium heat, add the olive oil.
Season the potatoes with salt and pepper. When the oil is hot add the potatoes. Saute for about 4 to 6 minutes or until the potatoes start to brown. Season the fillets with salt and pepper. Season the cornmeal with Essence. Dredge the fillets in the cornmeal, coating completely.
In another large saute pan, over medium heat, add the vegetable oil.
When the oil is hot, pan-fry the fillets until golden, about 4 minutes on each side. Add the onions and continue to saute for 4 minutes.
Add the parsley to the potato mixture. Mix well.
Remove the fillets and drain on paper towels.
To serve, spoon the ravigote in the center of each plate. Spoon some of the potatoes in the center of the sauce. Lay the fillets directly on top of the potatoes. Garnish with green onions.