Heat the olive oil in a large pan and cook the chorizo and onion over a medium heat for 10 minutes until the chorizo has released lots of oil and the onion is soft. Add the garlic and cook for 2-3 minutes, then tip in the stock and potatoes. Simmer gently for 15 minutes until the potatoes are soft. Tip in the kale and cook for 2-3 minutes or until softened, adding a little water if it gets too thick. Season with salt and lots of black pepper, and spoon into bowls.