Need a vegetarian solution to a pureed vegetable soup that calls for chicken broth
I'd use vegetable broth, water, or a mixture of both.
I think if you compensate for the salt content of commercial chicken stock (taste first), up the herbs in the recipe to taste, and add a little extra fat (preferably butter), you'll have what might be missing.
Two non-meat ingredients that can increase the savoriness of a vegetable broth are mushrooms and tomato paste. Browning the tomato paste makes it even better. When I've added these components to a vegetable broth the difference has been substantial (and delicious).
I often find vegetable broths to be too sweet. I'm a huge fan of using this mushroom stock: http://www.epicurious.com...
I keep this vegetable bouillon on hand at all times. Use it in everything. It has a nice spice to it, and is not sweet. It is from 101cookbooks via The River Cottage Preserves Cookbook http://www.101cookbooks...
And you can add what vegetables you like. For example, cilantro is not my thing so I use more parsely. When I don't have celeriac and shallots on hand, it is onions and celery.
I don't like most commercial vegetable stock, too much green pepper. Rapunzel boullion is pretty good. I sometimes make my own, tailored to the flavors I want. I also love mushroom stock for anything needing a heartyness/meatiness or earthiness. Definitely want to enhance seasonings if you taste it and it's missing something.
If you're looking to buy one, Pacific used to make an organic "No Chicken" broth that was great. I say "used to" because I haven't been able to find it the last few times I looked for it but I'd keep an eye out for it. I also really dislike commercial vegetable broth.