Cucumbers wash, peel, halve lengthwise and scrape out the seeds with a spoon. Cut the cucumber halves into slices. Peel onions and dice one roughly. Heat half of the fat in a pot and fry the onion cubes in it until translucent.
Add cucumbers, braise and deglaze with stock and vinegar. Season with salt and pepper, bring to the boil, cover and stew for ten to 15 minutes. Cook rice covered in 1/2 litre boiling salted water for 20 minutes.
Clean, wash and cut the carrot into pieces. Bring 1/2 litre salted water with carrot, bay leaf, lemon slices, mustard and peppercorns to the boil and simmer for five minutes. Wash the fish, place in the stock, cover and simmer at low heat for 15 minutes.
Wash the dill, dab dry and cut finely, except for a little to garnish. Finely dice the remaining onion. Heat the remaining fat in a pot and fry the onion cubes in it until transparent. Sweat mustard and deglaze with cream.
Season to taste with salt, pepper and sugar. Thicken slightly with sauce thickener. Drain capers and add. Drain fish and arrange on a plate together with the cucumber vegetables.
Pour some sauce over it, sprinkle with dill and serve garnished with dill blossom as desired. Add the rest of the sauce and rice.