How would one make the best vegetable stock for this soup? I'm putting this on the menu for a special dinner coming up. Thank you. ;o)

I am SO glad you asked this question. I made this soup last week, and I kept thinking that a Keller soup recipe really required a more Keller-worthy broth than what I threw together.

The Cook's Illustrated article drbabs mentioned is interesting. It recommends celery root (mild yet complex), leeks (low sugar, neutral), freeze-dried onion (for depth--but how Cooks Illustrated!), tomato paste (savory depth without identifying as a tomato). They suggest no celery (bitter and sour), onions (sulfurous and sweet), tomatoes (mild and watery), sun-dried tomatos (sweet-sour). They also add soy sauce (umami, and it worked better than shiitake mushrooms or kombu). I'm not sure whether to give it a go or not. But I'm looking forward to hearing what you decide.

This month's Cooks Illustrated has a recipe for vegetable broth that I think would work fine. Do you get the magazine? Here's a link to the recipe: http://www.cooksillustrated.com/recipes/8204-vegetable-broth-base?incode=MCSCZ00L0

If you can't open it, message me privately and I'll send it to you.

I love sweating onions until sweet, adding the usual carrot and celery AND the guts from any winter squash. It makes a beautiful and tasty golden broth.

Butternut seems to work the best. I made acorn squash dog biscuits this morning and my small acorn squash had mostly seeds and the strings were very pale.

HLA, I like the idea of mushroom stock. Is that recipe available only in the book?

AJ - I really like the mushroom stock recipe from Fields of Greens. It's rich and not too sweet, so I think it will work well for a butternut soup. http://www.epicurious.com/recipes/food/views/Mushroom-Stock-15319