BRING water, chopped cauliflower, butter and salt to boil in saucepan on medium heat; simmer on medium-low heat 30 min. or until cauliflower is tender.
STIR in milk, cream cheese and cheddar; cook on low heat until cheeses are melted, stirring constantly. Remove from heat. Puree until smooth; return to stove top. Cook until heated through.
FOR each serving: Ladle 1 cup soup into bowl. Garnish with 2 sauteed cauliflower floret halves and 1 tsp. chives.