Pre-heat the oven to 350 degrees. Cut the celery root into very fine slices then the slices into fine julienne strips. Toast the walnuts in the preheated oven for 6 minutes or until they start to turn light brown remove the walnuts from the oven and rub in a towel to remove any loose skin. Cut the black olives into slivers. Mix the celery root, walnuts, black olives, sherry vinegar, olive oil, 2 tablespoons salt, freshly ground pepper together. Let sit for 30 minutes for the flavors to marry. Season the rouget fillets with salt and pepper then dredge in the flour. Heat 3 tablespoons clarified butter in a saute pan and cook the fish until golden flip and cook the other side.