1. Beat egg whites until frothy.
2. Gradually add half of sugar and continue beating until stiff.
3. In a separate bowl, beat yolks, rest of sugar, potato starch and lemon juice.
4. Fold yolk mixture into whites. Add almonds and grated apple and combine gently.
5. Bake in a tube pan or 10×14-inch baking pan for one hour at 350 degrees Fahrenheit.