Just wanted to mention another spelling for that soup. It is Vichyssoise, as the aforementioned spelling doesn't fit correctly into the surrounding clues. Noticed this especially with 26a Former name of Demo. Repub. of the Congo from 1971-1997 = Z?S?E. With the spelling above, the solution has = Z?I?E which leads to Zaire of course.
Thanks for steering us in the right direction, Imur. All the best...Dogz