In a large heavy-bottomed pot or Dutch oven, melt 1 tablespoon of the butter over medium-high heat. Add the onion and cook until translucent, 2-3 minutes. Add the rice and cook another 2-3 minutes, stirring frequently.
Add the wine, and stir for about 1 minute. Reduce the heat to medium, and begin adding the stock about 1/4-1/2 cup at a time, stirring almost constantly and allowing the rice to absorb the previous addition before adding more.
When about half of the stock has been added, add the corn to the pot and continue with adding the stock as before. When most of the stock has been used, begin tasting periodically - when the rice is almost completely cooked through, add one last addition of stock, and when the risotto is still creamy, add the last tablespoon of butter and the Parmesan cheese, stirring to combine. Taste for seasoning, and serve garnished with a bit of green onion, if desired.