Using a sharp knife, cut the washed kale leaves off their stems. Slice the leaves thinly then chop roughly.
Heat the olive oil in a large soup pot, add onion, garlic, chili, bay leaf and salt, and cook over medium heat for three to four minutes, stirring frequently.
Add the potatoes and nutritional yeast, if using, plus a cup of the water or stock. Stir and cover to cook for five minutes.
Add the kale, cover and steam until it is wilted, stirring occasionally.
Pour in the rest of the water or stock (I use Marigold bouillon powder) and bring to the boil and simmer, covered, until the potatoes are quite soft, 30 to 30 minutes.
Use the back of a wooden spoon to break up the potatoes against the side of the pot or puree and cup or two in a blender and return it to the pot.
Taste for salt and add a generous grinding of pepper. If possible let the soup sit for an hour or so before serving to allow the flavours to further develop.
Serve without any garnish.