Put the buckwheat groats into a dry pan and roast over a gentle heat, until turning brown and smelling toasty.
In a large frying pan, saute the onion, leek, celery, and garlic in olive oil until translucent. Add the toasted groats and stir so they can absorb the flavors. Pour over the stock and simmer until buckwheat is tender.
In a separate pan, saute the mushrooms in olive oil until soft and juicy. Add to the buckwheat and other vegetables and stir.
At the last minute, stir in the finely chopped raw kale and allow to wilt in the residual heat of the risotto. Serve.