Preheat the oven to 350°F (177°C). Line three 6-inch cake pans with parchment paper on the bottom. No need to grease the pans.
Separate egg whites and yolks, making sure not even a little bit of egg yolk gets into the whites. (TIP: It's easier to separate an egg when it’s cold right out of the fridge.)
In another mixing bowl with whisk attachment, beat egg whites at medium low speed until foamy. Add ½ cup of sugar 1 tablespoon at a time and continue to whisk until stiff peaks, gradually increasing the speed to medium high, 7-10 minutes.
In a mixing bowl with a whisk attachment, whisk together egg yolks and the remaining ½ cup of sugar until pale and tripled in volume, about 5 minutes.
Using a spatula, add 1/3 of the whipped egg whites into the egg yolk mixture and gently fold until mostly smooth. Add the remaining egg whites and gently fold until smooth.
Sift flour and salt into the egg mixture and gently fold the batter until all the flour is evenly incorporated.
Evenly divide the batter into the prepared pans and smooth the top. Tap the pans a few times on the counter and then run a butter knife through the batter to remove any trapped air pockets.
Bake the cakes until inserted toothpick comes out clean, 25-30 minutes. Don't open the oven for at least the first 20 minutes!
Let the cake cool for 5 minutes in the pan. When the pan is cool to touch, run a knife around the edges of the pan and invert onto a cooling rack. Peel off the parchment paper and cool the cake completely. Once cooled, wrap with plastic wrap and refrigerate, preferably overnight. It'll be easier to slice when the cake is thoroughly chilled.