Or, to be pedantic, potato and watercress, since there was more potato than watercress.
I used a pouch of Knorr Chicken soup (other brands are available), Jersey royals (scrubbed), and watercress, and added a touch of salt and a good slug of milk.
Sam looked at it and said ‘no, thanks’, but when he tasted it, said ‘yes, please!’. Even John (who doesn’t like watercress) had some. He said it was a nice light summery soup, and it was a pity we didn’t have a summer to go with.