1. Beat egg whites just until they form soft peaks in a large bowl.
2. Beat egg yolks, one at a time, into hot mashed potatoes in a second large bowl; stir in the cheese, chives, parsley, pimiento and liquid red-pepper seasoning. Fold in beaten egg whites until no streaks of white remain; spoon into a buttered, 6-cup baking dish.
3. Bake in moderate oven (375°) for 40 minutes, or till puffed and golden.