You may have heard of beer can chicken where the chicken is roasted and also cooked from the inside by the steaming beer? Well there's no reason us vegetarians should miss out on this great way of cooking!
Cut the bottom off the butternut pumpkin and hollow out the pumpkin so that there is enough room to sit the entire pumpkin comfortably on top of the beer can. You can add some herbs to the remaining beer in the can if you like.
I just cut the top off the pumpkin and made some inserts with a knife through the flesh of the pumpkin from the top to the bottom. I'm not sure if this is necessary but the pumpkin has quite dense flesh so I just wanted to create some vents so that steam from the evaporating beer could escape. Then sit the pumpkin on the beer can and make sure the whole thing is quite stable.
Then just put the whole thing in the oven along with your roasting potatoes and whatever else you are serving with the pumpkin. Be careful to sit it on a flat surface and don't slam the oven door too hard as it can fall over quite easily! I put mine in for about 50 minutes and this seemed fine.