Place the fish in a food processor along with the mirepoix and process until finely chopped. Transfer this to a saucepan, add the egg whites and peppercorns and stir in well. Gradually add the cold stock and the white wine, stirring continuously.
Bring to the boil over a high heat, stirring frequently to prevent it from sticking. Stop stirring just before the consommé boils. Once it has started to boil, turn down the heat so that it is barely simmering, and allow to simmer for 30-40 minutes.
Carefully strain the consommé through muslin or a fine strainer – the finished consommé should be absolutely crystal clear. Use within a few days.