Using a brush, oil the two shelves in the steam tray.
Cut the potatoes into cubes (3-4 cm) and place on the lower shelf. Divide the cod into four pieces (200 g each) and place on the lower shelf. Season with salt and pepper to taste and put to one side.
In the bowl place the chopped onion, garlic, 30 g oil, wine, tomato quarters, water, salt and pepper and grind for 30 seconds on speed 10.
Place the steam tray on top of the bowl and programme for 30 minutes on the Steam function.
Serve the cod and potatoes with the sauce.
To offset the acidity of the tomato, you can add a pinch of sugar.