Using a paper towel and a dab of butter, wipe the inside of a big baking pan (I used a Pound Cake / Angel Food Cake Pan) and then sprinkle a thick coat of almond flour on it. If you don't do this, the cake could stick (like mine did for this photo) and you'll be cursing and trying to fix it :)
Sift the potato and baking powder, mix them together and set aside. Using an electric mixer, beat the eggs until they are a light color and a creamy, fluffy texture.
Add the sugar, one spoon at the time, and continue to whip. The mixture should double the volume. The whipping time will depend of the speed of your mixer, it took me about 7 minutes.
Next while still mixing add the potato starch, vanilla and lemon zest.
Melt the ⅞ cup of butter and add it to the batter, mixing until all ingredients are combined.
Pour the batter into your prepared baking pan (it should not take more than ⅔ of the pan, as the cake will grow a lot).
Bake at 320F for first 30 minutes. After that time increase the temperature to 340F and bake for another 20 minutes or until an inserted toothpick comes out dry.
When done, remove from the pan and let it cool for few minutes.
Dust with icing sugar before serving.
Recipe by Costco Diva at http://www.costcodiva.com/light-as-air-gluten-free-easter-cake/