Preheat the oven to 350F (177C) convection (325F/163C conventional) and grease and line four 9-inch* pans with baking spray and parchment paper.
Place the egg whites in the bowl of the stand mixer and using the whisk attachment, at full speed, beat until they're frothy.
12 large eggs
With the mixer on medium speed, stream in the sugar. Turn the mixer up to full speed and beat just until the meringue reaches stiff peaks.
300 grams (1 1/2 cups) granulated sugar
Pour in the egg yolks and vanilla and turn the mixer to medium-high speed, mixing, a few seconds, just until they're fully combined.
2 teaspoons vanilla extract
Sift in the flour and salt (and baking powder if using) and turn the mixer up to medium-low speed, mixing just until the flour is incorporated.
240 grams (2 cups) all-purpose flour, 1/4 teaspoon fine sea salt, 2 tsp baking powder
Scrape the edge of the bowl well and distribute the batter evenly among the four pans, about 10.5 ounces each, and bake for about 15-18ish minutes, until the cake is golden and separates itself from the edge of the pan. It will also spring back when you press on it gently.
Flip the cakes over onto a tea towel and allow them to cool completely (I don't recommend flipping onto a wire rack, mine got suck on there before).