Slice off cauliflower base & discard the discolored outer leaves. Thinly slice the remaining leaves & break the cauliflower into florets. Wash & drain well.
Heat the oil in a soup pot & saute the cauliflower & onion over medium heat, covered, for 10 minutes. Do not allow to brown. Add ginger, stock, salt & pepper. Bring to a boil, cover & simmer for 30 minutes. Cool slightly.
blend cooled soup in a blender or food processor until smooth. Return to pot & heat until warmed through. Serve immediately.
Elizabeth Brand, "Vegetables"