Mashed potatoes: Chop potatoes into quarters and boil in water until soft, 15 to 20 minutes. Drain, then mash and stir in butter and milk. Salt to taste.
Lemon cream sauce: Combine the sauce ingredients in a small saucepan and warm gently – do not boil. Whisk until smooth.
Pan-fried whiting: Ceat a non-stick pan on medium-high heat. Add oil and butter – you want a good layer of oil so the fish doesn’t stick.
Pan-fry the first five whiting fillets starting skin-side up for a minute. You want a touch of golden colour on it. Flip the fillets carefully and fry skin-side down for another minute or two, until flesh is just cooked through.
Remove the cooked fillets and set them aside on a plate while you cook the second batch. Once fish is cooked, remove it from the pan and turn off the heat. Throw the finely diced onion into the still-hot oil in the pan and toss it around until translucent. You’ll have crispy broken bits of fish too – yum, it’s all good!
Serving up: Stir half of the lemon cream sauce into the mashed potatoes, and pile onto one side of a platter. Sprinkle cooked onions on top of the mashed potato.
On the other side of the platter, lay out the rocket leaves. Lay all the cooked fish on top of the rocket. Sprinkle the parsley over the platter. Add the lemon slices and serve with the remaining sauce on the side.