5 issues of BBC Good Food for £5
Tip the onion and chopped dill into a bowl with the horseradish and lemon juice. Stir through the soured cream, season with a pinch of salt and generous grinding of pepper, and mix well. Can be made a day ahead and kept in the fridge.
Arrange the salmon on a board or plate, scatter with the remaining dill fronds and serve with a grinding of black pepper and the sauce alongside.