Melt the butter and add to the mash potato, mix in well and season with salt and pepper.
Sift the flour into the potato and mix into a dough.
Roll out on a floured surface until approx 1/4 – 1/2 inch thick.
Cut into rounds using a scone cutter.
Cook in a very hot, lightly oiled pan or griddle until brown on both side.
Place one spoonful of crème fraiche on each potato cake, and arrange a generous slice of mackerel on top. Garnish with lemon wedges and sprigs of dill or parsley.
Sour cream can be used instead of crème fraiche.
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