Heat the olive oil in a deep, heavy-based frying pan or sautee pan. Gently cook the onion and garlic until they are soft but not coloring at all. This should take about 5 minutes. Stir in the chicken, and fry for 3-4 minutes.
Add the rice and rosemary and stir for about a minute until the rice looks slightly translucent. Pour in the wine and stir continuously until it has cooked into the rice. Add a good ladle of hot stock and season with salt and pepper. Turn the heat down so the risotto is simmering gently and then keep adding ladles of stock as it cooks into the rice, stirring and moving the rice around in the pan.
After about 12-15 minutes, stir in the Broccolini and continue stirring and adding the stock for 5-8 minutes until the rice is soft but still with a bit of bite left in it. The texture of the risotto should be thick and creamy, but not too loose. Add extra stock or hot water if necessary.
Remove the cooked risotto from the heat, and stir in the parmesan cheese and add any extra stock if the risotto seems particularly thick.