Heat the broth in a pot and keep it warm over low heat.
In a large pan, heat the olive oil over medium heat. Add the chopped onion.
Add minced garlic and sauté for about a minute until fragrant.
Stir in Arborio rice, coating it in the oil and heating it until slightly translucent.
Pour in a ladleful of warm vegetable broth, stirring continuously until absorbed.
Once absorbed, add another ladle of broth and repeat the stirring process, continuing until the rice is al dente.
Add pumpkin puree and nutmeg, stirring to combine well.
Continue cooking and adding broth until the mixture reaches your desired creaminess, usually about 20 minutes.
Remove from heat and stir in grated Parmesan cheese until melted and well combined.
Season with salt and pepper to taste and serve immediately, garnishing with fresh sage leaves if desired.