Peel the kohlrabi and finely chop the leaves discarding the stems. Cube the kohlrabi along with the carrot and potatoes. In a large pot heat up 1 tablespoon of oil, add the onion and gently cook for 3 minutes until softened. Add the rest of the vegetables along with the parsley and cook for a few minutes stirring often.
Add the vegetable stock, pepper to taste, stir, cover and bring to the boil then lower the heat and simmer for about 30 minutes or until the vegetables are tender, stirring occasionally.
Stir in the chopped dill and cook for 3 more minutes. At this point you can also thicken the soup (but you don’t have to). To do this dissolve corn starch in 2 tablespoons of hot water then add this mixture into the soup and cook for 3 minutes.
Remove from the heat, adjust the seasoning if needed, stir in a tablespoon of butter and serve (either as it is or with a dollop of yogurt/sour cream).
When shopping for kohlrabi choose medium-sized bulbs as they are sweeter than very large ones.
Ensure the vegetables are roughly the same size (once cubed) so they cook evenly.