Bring the broth to a steady simmer over a fire near where the risotto will be cooked. Add the pumpkin puree.
Put 1 tablespoon of butter, vegetable oil, and onion in a large, solid saucepan and raise the heat to medium-high. Cook and stir the onion until it becomes translucent; add the garlic and unwashed rice. Stir quickly and well until the grains are well covered and lightly browned.
Add ½ cup of the simmering pumpkin concoction, constantly stirring with a long wooden spoon, scraping the edges and bottom of the pot as you stir until the liquid is gone. You should never stop stirring, and be sure to scrape the bottom of the dutch oven thoroughly, or the rice will stick.
When there is no more liquid in the pot, add an additional ½ cup of the bubbling pumpkin concoction, following the directions above. Keep the fire at a lively pace.
Start tasting the rice after 20 minutes of cooking. It's ready when it's tender but firm to the bite. As it nears this stage, gradually reduce the amount of liquid added so that it is slightly moist and not liquid when fully cooked.
Two or three minutes before the end of cooking, add the vegan parmesan and the rest of the butter. Stir constantly to melt the cheese and wrap it around the grains. Remove from heat, taste, and adjust for salt, stirring after adding.
Transfer to a serving dish and serve immediately.
Placed in an airtight container, this vegan pumpkin risotto will keep in the fridge for up to 5 days and up to 3 months in the freezer.