Prep the vegetables: Finely chop the onion and garlic, keeping them separate. Remove the seeds and stringy pulp from the pumpkin and cut the flesh into large pieces. Coarsely grate it using a food processor. Alternatively, cut the pumpkin into small cubes (see note).
Sauté the onion and garlic: Melt the 20 g (1 ½ tbsp) vegan butter in a large pot over medium heat. Sauté the onion until translucent. Add the garlic and cook for about 30 seconds.
Toast the risotto rice: Add the risotto rice and cook for 1–2 minutes, stirring, until the grains begin to look slightly translucent.
Deglaze with wine: Deglaze the risotto rice with white wine and let it simmer for about 1 minute, stirring constantly, until the wine has mostly evaporated.
Add the pumpkin: Add the grated pumpkin and stir it well into the rice.
Cook the risotto: Add enough warm vegetable broth to just cover the rice and pumpkin. Simmer over medium-low heat, stirring regularly. Once most of the liquid has been absorbed, add another portion of broth. Continue in this way until the rice is creamy but still has a little bite, about 20 minutes. If necessary, add a little more broth or water.
Finish with the mantecatura: Remove the pot from the heat. Stir in the salt, pepper, freshly grated nutmeg, and nutritional yeast. Add the cold cubes of vegan butter and stir vigorously until the risotto is wonderfully creamy. Taste and adjust the seasoning if needed.
Serve: Serve the pumpkin risotto immediately. If you like, top with roasted and salted pumpkin seeds (pepitas), a drizzle of pumpkin seed oil, and fresh herbs (cress, parsley, or dill).