Preheat your oven to 375°F/191°C.
Line a 9" by 13" baking sheet with parchment paper.
In a large bowl, combine egg yolks, 40g sugar, a pinch of salt, vegetable oil, milk, black sesame powder, and vanilla extract.
Sift in cake flour, stir until just mixed, and set aside.
Using a stand mixer with a whisk attachment, whip egg whites until foamy on medium-low speed.
Add cream of tartar and increase the speed.
Gradually incorporate the remaining 40g sugar until you reach soft peaks in the egg white meringue.
Gently fold 1/3 of the whipped egg white meringue into the black sesame egg yolk batter to lighten it with a spatula.
Continue folding in egg whites in 1/3 increments until fully incorporated.
Pour the batter into the prepared baking tray.
Tap the tray on the counter to release any air bubbles.
Smooth the surface with an offset spatula.
Bake at 375°F/191°C for 13-15 minutes until the top is springy and dry to the touch.
Remove the cake from the oven and tap the tray on the counter to prevent shrinkage.
Transfer the cake to a wire rack to cool, not completely.
Whisk until well combined.