1. Preheat oven to 350 degrees Fahrenheit (175 degrees Celsius).
2. Add the whole egg to the yolks.
3. In a stand mixer, beat the egg whites, gradually adding sugar, until soft peaks form.
4. In a small bowl, beat the whole egg and yolks with lemon juice. Slowly fold the yolks into the whites.
5. Sift potato starch into batter, one third at a time, folding gently after each addition. Gently fold in add-ins, if using.
6. Pour batter into an ungreased tube pan and bake for one hour and 10 minutes. Invert cake to cool.
7. If desired, make the glaze: Mix ingredients together, starting with one and a half cups confectioner’s sugar. Add more until you reach desired thickness. You don’t want it too runny. Spread over the cooled cake.
– Beat egg whites only until soft peaks. Soft peaks will continue to grow while baking, while stiff peaks are more likely to collapse.
– Use egg whites at room temperature, as they’ll beat up more nicely.
– Do not grease the tube pan and be sure to invert to cool.
– Fold gently! The goal is to retain as much of the whipped volume as possible. If you dump all the ingredients on top of the beaten whites, they will deflate.