Line the bottom of an 8-inch round cake pan with parchment paper If pan has a removable rim, wrap outside with foil to prevent water from seeping in.

In a large bowl, with a mixer on high speed, beat whole eggs, egg white, and sugar until thick and pale yellow, 4 to 5 minutes. Stir in vanilla.

In a small bowl, mix cake flour and baking powder until blended. Using a whisk, fold flour mixture into egg mixture until evenly blended. Pour batter into pan. Tap pan lightly on work surface to remove any air pockets.

Set a steamer rack; your steamer should be wide enough to hold cake pan without sides touching). Pour water into steamer/pot to about 1/2 inch below top of rack. Cover steamer and bring water to a boil over high heat.

Place cake on rack and cover steamer; reduce heat to medium and steam until a toothpick inserted in center of cake comes out clean, 20 to 25 minutes.