In a 4-quart saucepan, combine cauliflower, water and salt; bring to a boil. Reduce heat and let simmer until cauliflower is tender; let cool slightly. Transfer 2 cups cauliflower (including cooking liquid) to blender container and process until smooth. Repeat procedure, 2 cups at a time, until all cauliflower and cooking liquid have been processed. Set aside. In same saucepan heat margarine over medium-high heat until bubbly and hot; add onion and saute until translucent. Sprinkle with flour and broth mix and stir quickly to combine; cook, stirring, for 1 minute. Gradually add milk and cook, stirring constantly, until flour mixture is completely dissolved and liquid thickens; stir in pureed cauliflower. Reduce heat and let simmer, stirring occasionally, until heated through; stir in pepper. Ladle into 4 soup bowls and, if desired, sprinkle each portion with dash nutmeg.
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