Peel and boil potatoes. Cut into slices once cooked and cooled a little. Divide into 3 portions.
Peel and slice onion. Sauté lightly in the rapeseed oil. Do not brown.
Grease an ovenware dish.
Cover base with potato then add a layer of onions, salmon and dill.
Repeat and finish with a layer of potato.
Whisk together remaining ingredients and pour over salmon.
Bake for 30-40 minutes until the mixture feels firm.