4 oz. (3/4 cup plus 2 Tbs.) unbleached all-purpose flour
1 tsp. baking powder
3 large eggs, at room temperature
3 large egg yolks, at room temperature
3/4 cup granulated sugar
1 tsp. pure vanilla extract
1/8 tsp. table salt
1/4 cup whole milk
1 oz. (2 Tbs.) unsalted butter, cut into smaller pieces
Pan: 13x18 inch sheet pan, lined with parchment paper
Whisk the flour and baking powder in a medium bowl.
With an electric mixer (hand-held or a stand mixer fitted with the whisk attachment), beat the eggs, yolks, sugar, vanilla, and salt at high speed until the mixture has tripled in volume and forms a slowly dissolving ribbon when the stopped beater(s) are lifted, 4 to 6 minutes.
Meanwhile, heat the milk and butter in a small saucepan over medium heat until very hot but not boiling. Or heat in the microwave until butter is melted and milk is hot.
Using a fine-mesh sieve, sift one-third of the flour over the eggs. Fold with a large silicone spatula until the flour is blended into the batter. Repeat with two more batches.
Pour all of the hot milk mixture over the batter and fold gently with the silicone spatula, scraping the batter up from the bottom of the bowl and rotating the bowl, until the milk is incorporated. Scrape the batter into the pan and spread evenly.
Bake until the cake is golden and a tester inserted into the center comes out clean, 10 to 12 minutes. Set the pan on a rack to cool. After the cake has cooled completely, run a small knife or offset spatula around the inside of the pan, pressing against the pan to avoid tearing the cake. Invert the pan to remove the cake, and peel off the parchment liner. Turn the cake right side up.