For the green vegetable soup, wash the vegetables, peel the onion, kohlrabi, potatoes & ginger and cut everything into pieces. Heat the oil in a pot, fry the onion, garlic and ginger briefly, then add the rest of the vegetables and fry for 5 minutes.
Add the soup and simmer on low heat for 10-15 minutes. Puree the vegetables including the liquid with a blender, add sour cream if desired, season with salt and pepper and serve the green vegetable soup.