Preheat the oven to 350º F. Prepare two 8-inch baking pans by lightly buttering the sides and bottom. Line the bottoms with parchment paper.
Separate the eggs. Place the egg whites in a large mixing bowl and the egg yolks in a smaller mixing bowl. Set aside.
Sift together the flour and salt into a separate bowl. Set aside.
Beat the egg whites with a stand or handheld electric mixer until soft peaks form. Add 1/4 cup of the sugar and beat until stiff peaks form. Meringue should be glossy.
To the bowl with egg yolks, add the remaining sugar and vanilla extract. Beat using the electric mixer until the mixture is pale yellow and has a ribbon consistency.
Gently fold 1/3 of the whipped egg whites into the egg yolks. Pour the egg yolk mixture into the egg whites and fold until the mixture is homogenous.
Incorporate the flour mixture in two batches. Fold gently until no streaks of dry ingredients remain.
Pour the batter into the two prepared cake pans evenly. Smooth out the surface using a rubber spatula.
Bake the cakes in the preheated oven for 25 to 30 minutes, or until a skewer comes out clean when inserted. Remove the cakes from the oven and let them cool on a cooling rack with the pans upside down to prevent shrinkage.
When the cakes have cooled, wrap the sponge layers in plastic wrap and store in refrigerator until ready to assemble.