Preheat the oven to 350°F and line the bottom of a 9”x13” pan with parchment paper, leaving an overhang on two sides for easy removal.
In a medium bowl, whisk together the flour, baking powder, and salt. Set aside.
In a large bowl, whisk the egg yolks, vanilla and sugar until lightened and pale in color, about 3-5 minutes.
In a bowl of a stand mixer fitted with a whisk attachment (or using a handheld mixer with whisk beater) beat the egg whites until stiff peaks form, about 3-5 minutes. Set aside.
To the yolk-sugar mixture, add the dry ingredients & milk and mix together until just combined, about 15-20 seconds, just until some streaks remain.
Whisk 1 cup of the whipped egg whites into the cake batter, to help loosen the batter.
Fold the remaining whipped egg whites into the cake batter just until combined and no streaks remain.
Transfer the batter to the pan and spread into an even layer.
Bake for 20-23 minutes or until a toothpick inserted into the center comes out clean.
Allow the cake to cool completely on a wire rack for about 1 hour before proceeding.