Thoroughly mix the potato starch, cornstarch, baking powder, salt and xanthan gum. Set aside.
Beat egg yolks and sugar with electric mixer until thick. Add orange juice, vanilla and zest, mixing until it's just blended. Then add the dry ingredients mixture and combine together. Set aside.
Beat egg whites with cream of tartar until you see very stiff peaks that have formed. Fold egg whites into batter until just blended.
Pour into an ungreased 10 inch tube pan and bake at 325°F for 40 minutes.
Then turn heat up to 350°F for 5-10 minutes or until lightly browned.
Flip the pan and leave it until it's completely cooled.