World's simplest mushroom soup recipe

Accidentially discovered while making a stuffing precursor:

• One basket sliced mushrooms
• 3 cups or so of water
• One tea ball full of chopped fresh rosemary (probably optional)
• One heaping teaspoon Penzey's vegetable broth base

Rinse mushrooms; put in water in pot with tea ball. Boil for an hour. Add broth base; blend until pureed.

Astoundingly tasty for its simplicity; I now want to try it as actual soup, with a bit of cream added.