25g/1oz butter, softened, plus extra for frying
2 free-range egg yolks, plus 3 free-range egg whites, whisked until stiff peaks form when the whisk is removed
2 tbsp plain flour
4 tbsp double cream
salt and freshly ground black pepper
150-200g/5-7oz smoked salmon slices, to serve
To make the pickled red onions, place the white wine vinegar, sugar and salt into a glass bowl and stir until dissolved. Add the red onion slices and stir to coat them in the mixture. Cover the bowl with cling film and set aside for one hour.
For the sweet mustard dressing, whisk together the mustard, sugar and egg yolk in a bowl until well combined.
Gradually add the oil, a drop at a time at first, then in a thin stream, whisking continuously, until the mixture has thickened and is smooth. Season, to taste, with salt and freshly ground black pepper.
Stir in the chopped dill. Cover and chill in the fridge until needed.
For the potato pancakes, mash the cooked potatoes, using a potato ricer or masher, until smooth. Beat in the butter and egg yolks, then fold in the flour until well combined.
Gradually add enough cream to loosen the mashed potato mixture to a smooth batter. Season, to taste, with salt and freshly ground black pepper.
Carefully fold the whisked egg whites into the potato pancake batter until well combined.
Heat a knob of butter in a large frying pan over a medium heat. When the butter is foaming, add six spoonfuls of the potato pancake batter mixture to the pan, making sure to leave space between each spoonful.
Fry the potato pancakes for 2-3 minutes on each side, or until risen and golden-brown on both sides. Remove from the pan and keep warm. Repeat the process with the remaining batter mixture (there should be enough batter to make 12 pancakes).
To serve, place three potato pancakes into the centre of each of four serving plates. Arrange the smoked salmon slices on top, then drizzle over the sweet mustard dressing. Sprinkle the dill over the pickled red onions and serve alongside.
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