Remove the skin from the onion, chop finely and fry in the oil with the lentils, stirring for a few seconds. Add the vegetable soup, bring to a boil and simmer at low temperature with the lid closed for 20-30 minutes until the lentils are half soft. Add the diced potatoes, bring to the boil again and cook for another 10-15 minutes until the lentils and potatoes are cooked. Then add the whipped cream and heat to just below boiling point. Season the soup with salt and freshly ground pepper. Sprinkle with chives and savory.