Yum!

Ok - it worked! The roasted cauliflower soup turned out quite well - very tasty with a some crusty bread from Macrina on the side... here's the recipe:

Roasted Cauliflower Soup

1 med. head cauliflower
5-6 cloves garlic, peeled and sliced in half
3 Tbsp. olive oil
salt & pepper

3 med. leeks, green parts removed, rinsed well and sliced crosswise
1 Tbs. butter
1 Qt. (or so) vegetable stock (not a tomato-y one)
1/2 lb. yellow potatoes (I used Russian fingerlings), cut into 1 inch pieces
1/2 cup cream
salt & pepper to taste

Preheat oven to 375F. Remove leaves and tough bottom stem of the cauliflower - slice the cauliflower lengthwise into 1/2 inch slices, then break up the florets. Spread the cauliflower in one layer on a baking sheet - scatter garlic, and drizzle with olive oil, sprinkle with salt & pepper. 
Roast for about 15 minutes, then flip the cauliflower and roast for another 15-20 minutes. Cauliflower should be tender and browned in spots.

Meanwhile, melt the butter in a medium-sized pot over med-high heat - add leeks and saute until wilted and slightly browned. Add the stock, bring to a boil, then add potatoes. Cook until potatoes are done (about 15 minutes). Let cool for at least 10 minutes.

When cauliflower and potatoes are done and slightly cooled, put all into a food processor or blender - carefully (use a potholder or dish towel) pulse/blend until failry smooth (it will have some texture, since you didn't peel the potatoes). Return soup to pot and add cream (more, or less, or milk, or none to taste). Bring to barely a simmer, check for salt & pepper, and serve!

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This was inspired by Nida's "leftover soup" recipe that she posted a few weeks ago, as well as by a description of a pasta served at How to Cook a Wolf (new restaurant on top of Queen Anne, not the MFK Fisher book, although must have been inspired by it) - which I thought sounded good but was too full to try.