How to prepare a vegetable base using roasted squash for savory tomato-chunk soup I am looking to prepare a roasted squash soup base/stock. I plan on pairing the meal with a stout beer tasting. How do i go from roasted squash and asparagus to having a flavor dense but low volume soup base/broth/stock to pour over/mix with my onions on the initial sauté? 

The primary concern here is that I am going to be making a vegan, chunky tomato-based soup, but i want most of the flavor to come from the vegetable stock. As such, I don't want to have much water content and will be adding things like celery and corn later on. even if the stock will come out as a gravy I am not worried much about consistency as the soup will cook for about four hours.

(*) I am not fixed on squash necessarily if a lower water volume vegetable might help I will consider that an answer as long as it is savory and on par with squash's eathiness and can be roasted for use in a soup stock
Your base probably needs to be a roasted squash puree, I don't think it will work well just being used to flavor a stock. Normally you would add cream to roasted squash to make a soup, but I guess that wouldn't be vegan. Butternut squash is tasty for this (and very autumn/winter), if you haven't actually picked out your ingredients yet.

If you want to add asparagus flavor, you should consider toasting/grilling the asparagus first. Applying a dry heat to asparagus when cooking it will bring out a very savory flavor (a nice addition to a vegan dish), but just boiling it in liquid will make it taste "grassy". It all depends on what flavor you want out of it, really. Asparagus is really a spring/summer ingredient though, if you're really wanting to be "seasonal" with this dish.