Preheat the oven to 200c/400F/Gas 6.
For the parsnips, blanch in boiling water for one minute. Drain and transfer to a roasting tin, toss in olive oil and roast in the oven for ten minutes.
For the potatoes, heat a griddle pan and coat the potatoes in the oil and rosemary. Place on the griddle and cook for two minutes on each side, or until cooked through.
For the beef, heat a separate griddle pan. Rub the steak with the oil and the seasoning and place on the griddle. Cook for two minutes on each side, or until cooked to your liking. Remove from the heat and allow to rest.
Meanwhile, for the mayonnaise, blend the egg yolk in a food processor and gradually add the oil and white wine vinegar.
Once blended into mayonnaise, stir through the mustard and season to taste with salt and freshly ground black pepper.
To serve, place the potatoes on a warm dish, top with the roast parsnips and then add the steak. Finish with a dollop of mayonnaise.
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