1. Heat the stock. 2. Peel and dice potatoes and boil them in the stock until soft. 3. Peel the cucumbers and grate them coarsely. 4. Melt the butter and soften the grated cucumber. 5. Add to the stock and potatoes. 6. Taste and add a little brine if necessary- the soup should have a pleasantly sour taste. 7. Mix the sour cream with the flour and stir into the soup. 8. Season with salt and pepper. 9. Serve immediately without bringing back to the boil.
