Preheat the oven to 350°F (conventional) and line a 9x13" tray with parchment paper.
In egg yolks, add ½ cup sugar, salt, and vanilla. Whisk until light and fluffy.
Whisk in milk, then sift in flour, cornstarch, and baking powder. Whisk to combine (don't overmix).
In a separate bowl, whisk egg whites with cream of tartar until glossy peaks form.
Gently fold a third of the meringue into the egg yolk mixture, then add the remaining meringue.
Transfer batter to the pan and bake for about ~15 minutes. Let the cake cool.