Cake Batter. Preheat oven to 350° F. Grease the bottoms and side of a 9 inch springform. For easier release, line the bottom of the pan with parchment paper and grease it.
In a large mixing bowl, mix half the sugar (50 g. or ¼ cup) with the lemon zest, pressing the zest into the sugar with a rubber spatula or with your fingertips.
Separate the eggs, placing the egg whites in the clean bowl of a stand mixer and the yolks into the large mixing bowl with the sugar and zest.
Add the lemon juice to the egg whites. With your mixer’s whisk attachment, beat on medium-high until foamy. Slowly add the remaining sugar. Beat until stiff peaks form.
While the egg whites are beating, mix the yolks and sugar/zest mixture until well combined. Add the rest of the dry ingredients and mix just until combined so that the dry ingredients are just moistened. (It is ok if there are some clumps.)
Once the egg whites reach stiff peaks, mix about 1/3 of the whites into the rest of the batter. The batter will become more hydrated and smoother. Gently pour the remaining egg whites on top of the batter. Do not fold them in yet and quickly move to step 7.
Start Meringue Topping. With the same mixing bowl and whisk attachment (no need to clean them), beat the egg whites and lemon juice on medium-high until foamy. Slowly add the sugar and beat until the whites are smooth and glossy.
Return to Cake Batter. While the egg whites for the topping are beating, return to the cake batter bowl and fold in the whites that are sitting on top of the batter until there are no streaks of egg whites remaining. The mixture will likely still have some clumps of batter, and that is ok, as you do not want to overmix. Pour batter into prepared pan.
Return to Meringue Topping. Once the egg whites for the topping are smooth and glossy, add the zest and beat until combined. Stop the mixer and sift the cornstarch over the glossy mixture. Fold to combine. Pour approximately ¼ of the meringue topping over the batter and, with a metal spatula or a knife, massage it into the top of the batter. Pour the rest of the meringue topping over the cake batter in the prepared pan and spread evenly. If desired, you can use the end of a metal spatula to create a pretty design in the meringue.
Bake 35-40 minutes, until the meringue topping is lightly browned.