Preheat oven to 450 degrees. On a baking sheet, toss cauliflower with vegetable oil and 1 teaspoon salt. Spread out, and roast until the florets turn brown, about 25 minutes.
In a medium saucepan, melt butter over medium-high heat. Add onions, and cook until soft, about 5 minutes. Stir in curry powder, cauliflower, water, and broth; cover, and bring to a boil. Uncover, lower heat, and simmer 5 minutes.
Using a slotted spoon, transfer 3 cups cauliflower to a bowl, and set aside. Put remaining florets into a blender or food processor, add 1 teaspoon salt, and process until smooth. Stir puree into broth in pan, and reheat if necessary. Ladle soup into bowls, and top with reserved florets and parsley.