Heat a large heavy-bottomed pan over medium and add the olive oil. Once it shimmers and starts to smell fragrant, add the finely chopped onion. Sauté for 3-4 minutes until translucent and soft, with a gentle sizzle.
Add the rinsed arborio rice to the pan. Stir constantly for about 2 minutes, toasting the grains until they look slightly translucent at the edges and release a nutty aroma.
If using wine, pour it in now and stir until mostly absorbed, about 1-2 minutes. The rice will bubble gently and smell fragrant.
Begin adding the warm vegetable stock, about half a cup at a time. Stir constantly, allowing each addition to be mostly absorbed before adding the next, maintaining a gentle simmer. Continue this process for about 15 minutes, watching the rice become tender but still slightly al dente.
When the rice is nearly done, stir in the green peas. Cook for another 2-3 minutes until peas are bright green and tender, and the risotto is creamy.
Remove the pan from heat. Stir in the grated Parmesan and a tablespoon of butter until melted and glossy. Adjust seasoning with salt and pepper as needed.
Let the risotto rest for a minute or two. Then, serve immediately, garnished with extra Parmesan if desired, and enjoy the vibrant, creamy texture with bursts of sweet peas in every bite.
