Warm the broth in a pot until just below boiling, keeping it hot throughout the cooking process.
In a large pan, sauté finely chopped onion and minced garlic in olive oil over medium heat until they turn translucent and fragrant, about 5 minutes.
Add the Arborio rice to the pan and stir for about 2 minutes, allowing the grains to toast slightly and release a nutty aroma.
Pour in the white wine and stir until it is mostly absorbed, which should take about 1-2 minutes. The mixture will smell bright and slightly tangy.
Begin adding the hot broth a ladleful at a time, stirring constantly, allowing the rice to absorb each addition before adding more. Continue this process, stirring frequently, for about 20 minutes.
When the rice is tender but still has a slight bite, stir in the roasted pumpkin purée and a pinch of ground nutmeg to incorporate the vibrant orange color and sweet flavor.
Continue stirring for another 5 minutes, allowing the flavors to meld and the risotto to become creamy. The mixture should be thick but still slightly jiggle when shaken.
Remove from heat and stir in grated Parmesan cheese for added umami and richness, if using. Taste and adjust seasoning with salt and pepper as needed.
Let the risotto rest for a minute, then serve hot in bowls, garnished with fresh herbs if desired. Enjoy the creamy, velvety pumpkin risotto with its beautiful orange hue and comforting aroma.