Grub and clean the mackerel, rinse them and pat them dry with paper towels. Peel the rhubarb stalks, cut them into pieces and fry them in 40g of butter.
Cover and cook over low heat for 15 min.
Add the single cream, season with salt and pepper and let it stew for another 15 min. Season the mackerel with salt and pepper, roll them in the flour.
Heat the remaining butter in 2 non-stick frying pans and cook the fish for 4 min on each side.
Arrange the mackerel on serving plates, sprinkle with chopped chives and serve with the rhubarb sauce.