Cod and Arctic char, with their different complementary qualities, are both absolutely delicious.
Peel the cucumber lengthwise using a cheese slicer, leaving some of the peel on.
Slice the cucumber into a jar with a lid.
Add salt and sugar, put the lid on the jar and shake it until the salt and sugar are evenly distributed.
Lightly crush the mustard seeds in a mortar.
Place the vinegar and half of the mustard seeds in the jar with the cucumber and mix well.
Put the egg yolks and cucumber juice in the mortar with the mustard seeds. Mix well.
Whisk in the oil, initially one drop at a time, and then trickle it in. Continue until a thick sauce is formed.
Sprinkle the flour over the skin side of the fillets and fry in neutral frying oil in a hot pan until the fish is a nice golden brown colour on both sides and the meat flakes away when you prick it with a fork.
Serve the fish with the mustard mayonnaise and the cucumber salad.