Warm the stock in a saucepan over low heat. Keep it at a gentle simmer throughout the cooking process – this is crucial for proper risotto texture.
Heat olive oil in a large heavy-bottomed pot or Dutch oven over medium heat. Add the diced onion and cook for 3-4 minutes until translucent but not browned.
Add the garlic and cook for another 30 seconds until fragrant, being careful not to burn it as this will create bitterness.
Add the arborio rice to the pot and stir constantly for 2-3 minutes until the grains become translucent around the edges but remain white in the center. This toasting step is essential for developing flavor.
Pour in the white wine and stir constantly until almost completely absorbed, about 1-2 minutes. You’ll know it’s time for the next step when you can drag your spoon through the rice and it leaves a clear path momentarily.
Begin adding the warm stock one ladle (about ½ cup) at a time, stirring frequently and waiting until each addition is nearly absorbed before adding more. This gradual process should take about 18-20 minutes total.
After about 15 minutes of adding stock (when the rice is about halfway cooked), stir in the pumpkin puree, chopped sage, and nutmeg. Continue adding stock and stirring until the rice is al dente – tender but with a slight bite in the center.
Remove from heat and immediately stir in the goat cheese, Parmesan, and butter. This final stirring, called “mantecatura,” creates the signature creamy texture of risotto.
Season with salt and pepper to taste, remembering that the cheeses add saltiness already.
Let the risotto rest for 2 minutes before serving. Plate and garnish with optional toppings like toasted pumpkin seeds or fried sage leaves for added texture and visual appeal.