Preheat oven to 350℉ (180℃)
Lightly spray baking dish with baking spray
Place flour, baking powder and salt in a large bowl. Whisk together until well combined. Set bowl aside for later.
2 Cups All-purpose flour, 1 teaspoon Baking powder, ½ teaspoon Sea salt
Separate eggs into two bowls - a large bowl for the egg whites and medium bowl for the egg yolks.
5 Large Eggs
Using your mixer's whisk attachment, begin whipping the egg whites on medium speed and gradually increase to medium-high. Continue whipping until the egg whites are foamy and doubled in size.
Continue whipping egg whites while you pour in ¼ cup granulated sugar. Whip until stiff peaks form - this should take 2 - 3 minutes. Note - stiff peaks are reached when whipped egg whites hold their shape firmly and stand straight up without drooping when the whisk is lifted.
¼ Cup Granulated sugar
Add 1 cup granulated sugar to bowl with the egg yolks. Using a clean whisk attachment, begin mixing on medium-high speed until the yolks appear pale and well-risen (note - this should take 2 - 3 minutes).
1 Cup Granulated sugar
Add vanilla extract and milk to bowl with the egg yolks. Whisk together until well combined.
½ Cup Whole milk, 1 teaspoon Vanilla extract
Pour the flour mixture into bowl with whipped egg yolks. Gently fold with a spatula until no dry flour remains.
Add half the whipped egg whites to bowl with flour/egg yolks. Using a spatula, gently fold together until no white streaks remain.
Add the remaining whipped egg whites to bowl. Again, fold gently with a spatula until no white streaks remain.
Pour cake batter into prepared pan and smooth evenly.
Bake for 30–35 minutes. Test for doneness by inserting a toothpick into the center of the cake; it should come out clean.
Remove cake from oven and place on a wire rack. Cool for 20 minutes before proceeding with next step.