Preheat oven to 350˚F.
Butter baking pans. Line the bottom of each with a piece of parchment paper. Butter the paper and dust the pan with flour. (I only had 2 of these pans so I waited until one was baked and cooled and used it for the third cake layer.)
Using a whisk, blend together the 12 eggs yolks, 1 1/2 cups of sugar, milk, and vanilla. Stir until combined.
Add the flour and salt and whisk until combined.
In the bowl of a mixer on medium speed, whisk the 6 egg whites until you see soft peaks. About 2 minutes.
On low speed, add the remaining 3/4 cup of sugar slowly. Once all the sugar is added, turn the mixer on high and whip until you have stiff peaks. The mixture will have a glossy look to it.
With a spatula, gently fold 1/3 of the egg white mixture into the batter. Once combined, add the rest of the egg mixture to the batter and gently combine with the spatula.
Divide the batter into each of the baking pans (about 2 1/4 cups each). Using a rubber spatula spread the batter to flatten. Tap the pans on the counter to burst any air bubbles on the surface.
Bake the cake layers one pan at a time for 10-11 minutes.
Cool in the pan on baking racks.
Once cooled, flip the cake layer onto a piece of wax paper and remove the parchment paper.
If making the cake layers ahead, after they are cooled, wrap each in plastic wrap and keep in the refrigerator.