Thinly slice apples and cover the slices with lemon juice, sugar and cinnamon.
Beat yolks till creamy and thick.
Add potato starch and salt and beat well.
Add apple slices and mix to coat slices.
In a separate bowl, beat egg whites till they stand in peaks.
Fold whites into apple mixture.
Coat casserole dish with the oil and place casserole in oven to warm the dish.
After a few minutes, pour the apple mixture into the warm dish and bake about 35 minutes until custard is set.
Note: This can be made in a traditional souffle dish, in a deep quiche pan, or in separate ramekins. If ramekins are used, they should be baked in a water bath and checked for doneness after about twenty to twenty five minutes.