In a medium saucepan, bring the vegetable stock to a boil, reduce to a simmer and cover, and keep hot while you start the risotto.
In a large saute pan over medium heat, heat the olive oil and add the onion with a pinch of salt.
Cook for 2-3 minutes before adding the rice. Cook the rice, stirring, for another 3 minutes to allow each piece of rice to be coated.
Add the wine and stir for another minute. Add the sprigs of rosemary.
Stir in 1 cup of the stock and cook while stirring for 2-3 minutes until liquid has been absorbed.
1 cup at a time, add 3 more cups of the hot stock, waiting until the liquid is absorbed before adding each cup.
Stir in the pumpkin puree and a big pinch of salt. Continue the process with the remaining stock, 1 cup at a time, until the rice is tender, about 10 more minutes. The risotto should be loose and spill onto your serving plate.
Remove the rosemary stems and taste for salt, adding if needed.