Season the salmon with salt and pepper and rub with dill and mustard. Fry in a pan with oil.
Chop the onion very finely and fry it in a little olive oil with about the same amount of dill. Not too long, otherwise it will be bitter! Add 2 tablespoons of mustard and heat until the mustard becomes creamy. Add 1.5 cups of cream and season with salt, pepper, sugar and a squeeze of lemon juice.
Optionally, you can also add a little Worcester sauce to create a pleasantly sweet taste, as can be found in Scandinavian cuisine. Serve the salmon with the sauce, I love rice with it.