In a large saucepan, heat the olive oil over medium heat. Add the onion and garlic and cook until softened, about 5 minutes.

Add the arborio rice to the saucepan and cook for 1-2 minutes, stirring constantly, until the rice is well coated with the oil.

Pour in the white wine and cook until it has evaporated, stirring constantly.

Add a ladleful of vegetable broth to the saucepan and cook, stirring constantly, until the broth has been absorbed. Repeat this process with the remaining broth, one ladleful at a time, until the rice is al dente and creamy. This should take about 20-25 minutes.

Stir in the pumpkin puree, thyme, Parmesan cheese, butter, and season with salt and pepper to taste. Cook for an additional 2-3 minutes, until heated through.

Serve the pumpkin risotto hot, garnished with additional Parmesan cheese and fresh thyme leaves, if desired.