Cook the cabbage in boiling salted water until tender but still crisp, about 5 minutes.
Drain well.
In the top of a double boiler over hot water, blend together the egg, vinegar, butter, sugar, salt and pepper.
Cook, stirring, until thick, about 2.5 minutes.
Cool slightly.
Stir in the sour cream and green pepper.
Pour over the drained cabbage in a bowl.
Toss to coat well.
Serve warm or chilled, sprinkled with paprika.