2. In a mixer, whip the egg yolks on high speed while gradually adding half the sugar. Continue whipping until the mixture is thick and lemon colored, about 5 minutes. Add the juice and the zest.
3. Remove from the mixer and with a spatula, fold in the cake meal and potato starch.
4. Whip the egg whites on high speed while gradually adding the remaining half of the sugar. Continue whipping until medium peaks form, about 2 to 3 minutes. Gently fold the whites into the yolk mixture.
5. Spoon the mixture into an ungreased 10" tube pan with a removeable bottom. Bake until the cake is golden and springs back when touched, about 1 hour.
6. Invert the pan on its legs or over a bottle until it is completely cool. Remove from the pan and continue to cool on a cake rack.