Soak the chickpeas for at least 8 hours beforehand.When ready drain the chickpeas and add to a pressure cooker with the water and the olive oil. Put on a medium heat but do not cover or seal just yet, as the rest of the ingredients need to be added.Finely dice the carrots and celery and add to the pan.Peel the onion, kohlrabi and potato and add whole.Seal the pressure cooker and cook on a medium heat for about 30 minutes. If you are not using a pressure cooker then it needs about twice as long to cook, until the chickpeas are soft.Remove from the heat and wait for the pressure cooker to be safe to open.Get the onion, the kohlrabi and part of the potato together with some of the liquid and add to a blender. Add the yeast extract and miso paste to the blender and blend until smooth.Add this back to the soup and mix well.Add salt to taste. It is best to add the salt at the very end because otherwise the chickpeas will not soften properly.