Heat vegetable stock in a medium saucepan over medium high heat until it’s steaming.
Roughly chop 4 tablespoons (56 grams) of butter into small, ¼ inch (½ cm) pieces, and place in the freezer.
Melt the remaining 2 tablespoons (28 grams) butter in a large saucepan over medium heat. Add sage leaves and arborio rice to the saucepan, and toast the rice until it’s translucent, about 4–6 minutes. You don’t want the rice to take on any color, so turn down the heat if you see browning.
Add white wine, and cook until the rice has absorbed all the wine. Add in pumpkin, and stir until combined with the rice. Ladle ¾ cup (175 ml) hot stock into the large saucepan, just until the rice is covered. Once the rice has absorbed about half of the stock, add in another ½ cup (120 ml) ladle of hot stock. Continue this process until the rice is tender but still has a bite to it. From the time you add in the first ladle of hot stock, it should take about 16 minutes to fully cook the rice. Once ready, the rice will still look a little soupy.
Remove the risotto from heat, and remove sage leaves. Add the frozen butter to the rice, and stir until incorporated. Season with parmesan cheese, salt, and pepper. To serve, ladle the risotto on a plate, and tap the bottom of the plate to spread the risotto into a thin layer. Optionally, garnish with additional parmesan cheese.