In a BIG bowl, mix together the sour cream, oil, sugar, mustard powder and cider vinegar .
. Chop the onion very finely and add to this mixture.
Add salt and pepper to this mixture and set aside.
Slice the cabbage as thinly as you possibly can
Peel and grate the carrot,
grate the apple and slice the pepper thinly
Throw all vegetable matter into the bowl
Toss with the dressing.
Cover and let stand for at least an hour.
Toss again and serve