Beat the egg yolks, 2ounces (55g) sugar, and the lemon zest just to combine. Add the wine and vanilla. Gradually stir this mixture into the dry ingredients and mix until completely smooth. Refrigerate for about 30 minutes.
Just before the batter is to be used, whip the egg whites with the remaining 2ounces (55g) sugar until stiff peaks form. Gradually fold the reserved batter into the egg whites. For the best result, the batter should be used within 30 minutes. If you know you will not be able to use all of the batter right away, whip just 1 egg white with 1ounce (30g) sugar and add this to half of the reserved batter.