Bring two saucepans of salted water to the boil. Add the pasta to one pan and cook according to packet instructions. Drain, reserving a cupful of pasta water.
Meanwhile, add the kale (or cavolo nero) to the second saucepan and boil for 3 minutes. Drain.
Add the kale (or cavolo nero), lemon juice, garlic, chilli, parmesan, olive oil, and walnuts to a blender. Drain the beans into a bowl. Add the bean liquid and a third of the beans to the blender and blitz until completely smooth.
Add the pasta, remaining beans and sauce to a pan. Rinse out the blender with a splash of pasta water and add to the pan. Stir well and heat for a couple of minutes, or until warmed through. Season to taste with salt and pepper and serve with extra Parmesan!
