Pour the vegetable stock into a pot and bring it to a boil, lower the heat and let it gently simmer.
Place a pan on medium-low heat and add olive oil.
Add the shallots along with the garlic and gently sauté them until soft and translucent, without browning.
Stir in the rice and cook for a few minutes until they are semi-translucent. Make sure the grains are heated thoroughly before adding the wine. This stage is called tostatura; roasting the rice with the shallot before adding any liquid to it.
Add the white wine when the rice is hot enough and cook until all the alcohol evaporates. This stage is called sfumare when you add the alcohol to the hot pan and it bubbles away.
Turn the heat to low and start adding the simmering chicken stock a ladle each time.
Keep stirring the rice every 30-40 seconds until the stock is totally absorbed by the rice.
Add more stock when there is no more liquid in the pan and repeat the same process until the rice is nearly cooked but still crunchy.
Stir in the pumpkin purée, mascarpone cheese, salt, and pepper at this point and cook a few more minutes.
Check the rice and add more stock if necessary until it's cooked al dente. Stir in the roasted butternut squash.
Add the butter and give it a vigorous stir. This stage is called mantecatura; the continuous stirring of butter into the risotto to develop creaminess.
Turn the heat off and add the grated Parmesan cheese on top. Do not stir the Parmesan cheese in, and let the risotto rest for 5 minutes with a lid on.
Serve the risotto and garnish with chopped parsley or chives.