In large sauce pan boil florets in milk until tender, about 10 minutes. Set aside to cool. In separate sauce pan saute onion in butter. Add salt, potatoes, ham and broth. Cover and simmer for about 10 minutes. Add white pepper. Puree florets with some of the milk until smooth. Combine cauliflower mixture with potato broth mixture. Garnish with creme fraische.
For creme fraische, combine all ingredients in a bowl. Let sit for hours, preferably overnight.