For the pike in horseradish sauce, boil the water with salt, fish seasoning and onion, put the pike fillets in it and let them steep for 10-15 minutes.
Prepare a roux with butter and flour, add fish stock and milk and season with horseradish and a little sugar.
Let the steamed pike steep in the sauce for 10 minutes, add butter.
Arrange the pike in horseradish sauce in portions and serve.