Leek and potato soup, smoked salmon

Slice 1 small onion and 4 small leeks. Peel 2 small potatoes and cut them into small cubes.
Sweat onion and leeks in 25 gr butter. Add potatoes and 3/4 liter chicken stock. Boil softly for 20 mins. Add a good glug of cream. Blitz. Taste. Add water if too thick. Taste. Add pepper and salt to ones liking. Serve lukewarm with slivers of smoked salmon