Be sure to remove the leaves from the stems of the cavolo nero and slice the stems roughly. This will ensure the stems and leaves cook through in the same time.
Before steaming the cavolo nero, fry off the stems for a minute or two. Again this will ensure they cook through but also adds flavour to the final dish.
Before adding the wine or the vegetable stock, be sure to toast the rice for a few minutes in the hot pan. This adds a slight nuttiness to the flavour of the risotto.
When stirring through the cavolo nero puree, keep the heat and low cook only briefly. Any longer and you’ll lose that nice green colour.