For the rosti potatoes, grate the potatoes on a coarse setting onto a clean tea towel. Wring out the excess moisture by twisting the towel tightly around the potato and squeezing hard. Mix in 25ml clarified butter (see tips, below) or duck fat and season well. Do this quickly or the potato will start to discolour.
Heat the remaining clarified butter in a 20cm frying pan (or use individual mini rosti pans, like us). Add half the potato mix for a large one, pushing down with a spatula to ensure it evenly covers the pan. Or add a little in each individual rosti pan. Cook at a medium temperature for 8-10 minutes until you see traces of colour at the edges, then add a slice of haggis onto each individual rosti or 4 slices spread out if making one large one. Cook for another minute, then cover with more potato and lightly press down. Now carefully turn the haggis rosti over and cook until golden on both sides (5-6 mins). Transfer to a wire to cool. When cooled, cut a large rosti into quarters. This can be made in advance and left at room temperature until ready to use then reheated in a moderate oven (180C) for 5 mins.
For the dressing, mix the mustard, olive oil, vinegar, salt, pepper and chives together well, just before you’re ready to serve.
Heat a tbsp veg oil in a frying pan until hot and quickly sear the halved scallop rounds for 30 seconds on each side until golden. Season well and squeeze over a little lemon juice.
Toss the leaves in a little oil and lemon juice.
To serve, place a warm rosti on each plate, top with halves of hot scallop and a few dressed leaves. Drizzle the mustard dressing around the plate and serve immediately.
Tips on clarified butter: Clarified butter is just the oily part of butter, i.e. without the buttermilk. It gives potatoes a rich, buttery flavour. It will heat to a higher temperature than ordinary butter without burning. You can buy it ready prepared as ghee.
However, it’s easy to make: To make about 200ml, take 250g of unsalted butter and melt on a low heat in a small saucepan. Allow it to stand for a few minutes until all the oil rises to the top, then skim off the oil into a sealable plastic container. It will keep for 2 months in the fridge.