Solyanka Rӯbnaya

• white fish, ¾ kg (1½ lb) cleaned
• salt
• butter

Cut the cleaned fish into portion-sized pieces; cover them with cold water and bring to the boil, removing any scum. Then add salt to taste and simmer until done. Remove the fish and keep the bouillon hot. Meanwhile fry the onion in the butter, without letting it take colour, and add the tomato purée to it. Slice the gherkins and add them to the bouillon, followed by the cooked onion mixture, c