Wash the fish and dab dry. Sprinkle with lemon juice, salt and let it stand for about 20 minutes. Peel and quarter the onions. Bring 2 litres of salted water to the boil in a wide saucepan, add onions and bay leaf, simmer for about 10 minutes. Let fish chops simmer in it for about 10 minutes at medium heat. Wash the tomatoes, dab dry and cut into quarters. Wash parsley, shake dry, remove leaves and chop
Draw off 400 ml of fish stock. Melt butter. Sweat flour in it. Add cream and fish stock while stirring constantly, bring to the boil briefly. Stir in mustard and simmer for 2-3 minutes at low heat while stirring. Season sauce again with salt, pepper and sugar
Arrange fish chops, sauce, tomatoes and lemon wedges on plates and sprinkle with parsley. James serves a dry white wine with it