To finish the risotto (la mantecura):
Melt the butter in a heavy based pan, add the onion and fry until it becomes soft and translucent. Now add the rice and stir to coat it in the butter and toast the grains. Make sure they are all warm and only then add the wine. Let it completely evaporate until the onion and rice become dry.
Now is the time to start adding the warm stock, a ladleful or two at a time, stirring and scraping the rice in the pan. When each addition of the stock has evaporated, it is the time to add the new one.
Carry on cooking this way on a gentle to medium heat for about 15-20 minutes. After 15 minutes stir in chopped vegetables along with the lemon zest, add some salt, stir well and carry on cooking. I like the vegetables in the risotto to be still crunchy so if you would like to have them on a softer side, add them earlier on in the cooking process.
Taste the rice and cook until al dente, add more salt to taste. There shouldn’t be a lot of stock left in the pan, otherwise when you add the butter and cheese, it will become too soupy.
Once the rice is ready take it off the heat. Add the cold butter and Parmesan and immediately start stirring vigorously shacking the pan at the same time. Put the lid on and wait 2 minutes for the risotto to rest. It should have a creamy consistency. Serve immediately with some freshly grated black pepper and some extra Parmesan if required.