Place potatoes in a large pot with just enough cold water to cover them. Bring pot to the boil over a medium heat and cook potatoes till tender, about 40 minutes. Reserve 1½ cups of potato cooking liquid and drain the rest. Return the potatoes to a dry pot, stir over a medium heat until excess liquid disappears. Add 50ml olive oil and mash potatoes till smooth, use the reserved potato liquid to obtain desired consistency. Season with salt as needed.
To make the dill sauce, chop cornichons and dill together. Transfer to a bowl then stir through olive oil, chilli flakes and lemon juice. Set aside for flavours to develop.
Meanwhile, heat remaining 1 tablespoon of oil in a large frying pan over medium-high heat. Cook asparagus for 2-3 minutes or until lightly tender and charred. Remove from pan.
Return pan to a medium-high heat, add salmon, hold down the fish in the pan for a few seconds to ensure the skin stays flat. Fry for 2-4 minutes, or until skin is crisp, then lower heat, turn over salmon and continue to cook until to your liking.
To serve, spoon some potato mash onto four serving plates. Top with charred asparagus, crispy skin salmon and dill sauce.