Preheat oven to 350 degrees.

In a stand or handheld mixer, thoroughly combine butter and 3/4 cup of the sugar until light and fluffy. Add egg yolks, mixing thoroughly to combine. Add the lemon zest.

Sift together the flour, cornstarch, and baking powder. Slowly add to the butter and sugar mixture.

In a separate medium bowl, combine egg whites and remaining 1/2 cup of sugar. Using a standing or handheld mixer, whip to combine until airy and fluffy.

Gently fold egg white mixture in to batter, taking care to not deflate the egg whites too much.

Transfer to a 9 inch cake pan, which has been buttered and floured. Bake for 60 minutes.

Meanwhile, prep the lemon glaze. In a small saucepan, combine lemon juice with 1/2 cup of water and 1 tablespoon of sugar. Bring to a simmer for 5 minutes, or until sugar is completely dissolved. Remove from heat and allow to slightly cool.