Soak dried beans in ample water (they will double in size) for at least 12 hours, the drain and rinse, ready to cook.
In a large pot, heat 1 tablespoon olive oil and cook diced onion till soft and golden.
Add water and stock, dried beans, garlic, thyme, kombu and bay leaves. Cover, bring to a boil, then reduce to a simmer for about 40 minutes.
While the soup base cooks, wash kale, remove tough inner stalks, then slice into thin one inch ribbons – take your time with this, it is far nicer to have small delicate pieces.
After 30 minutes, add the potato, and leave to simmer for a further 10-15 minutes, at which point, both beans and potatoes should be soft. Fish out the bay leaves and kombu and discard. Now use a potato masher to carefully mash the beans/potatoes so about half of them are mashed and half whole (if beans/potatoes aren’t soft yet continue to cook a little longer).
Add kale, and cook for another 5-10 minutes. Note the water content – you may be just right, you may need to top up, or even cook uncovered to reduce it down.
By now, your total cooking time should be about an hour and ten minutes.
Once kale has just softened, add another tablespoon of olive oil, and stir in the lemon juice and zest. Serve with crusty bread and perhaps a sprinkle of nut parmesan!