In a wide medium sized saucepan, saute 2 tablespoons of butter and the chopped onion over medium heat, until the onions are lightly browned and soft.
Mix through the arborio rice and saute until lightly golden brown.
Add the white wine and cook until almost all the liquid is gone from the saucepan.
Over low to medium heat, add about ½ cup (125 ml) of stock to the rice mixture. Gently stir the rice through the mixture constantly until almost all the liquid has absorbed. Repeat until all the stock has been used up and the rice is soft and tender.
Remove rice from heat, mix through the grated parmesan cheese, lemon juice, lemon zest, remaining butter, and salt and pepper to taste.
Allow the rice to sit for 1 to 2 minutes with a lid on, then serve.
Notes
Use hot broth: When making risotto, it's crucial to use hot broth to keep the rice at the right temperature and ensure that it cooks evenly.
Constantly stir the risotto: This gives the dish its distinctive creamy texture by assisting in the release of the starch from the rice.
Add the broth in ladles at a time, waiting for the rice to soak up each batch before adding the next. This makes it easier to control how the rice cooks and keeps the dish from getting too soggy.
Give the risotto some time to rest: After the risotto is finished cooking, give it some time to rest before serving. As a result, the flavors can strengthen and the risotto gets even creamier.