Steamed Sponge Cake (Soy Zing Dan Gow)

This steamed sponge cake is a classic Chinese dessert that is deliciously served plain or with candied kumquats or citrus compote.
Line the bottom of an 8-inch round cake pan (with sides 2-3 inches high) with cooking parchment, cut to size. If the mold has a removable rim, wrap the outside with foil to prevent water from seeping in.In a large mixing bowl, beat the whole eggs, egg white, and sugar on high speed until light yellow and thick, 4-5 minutes. Add vanilla. In a small bowl, combine the flour and baking powder until smooth. Whisk the flour mixture with the egg mixture until smooth. Put the dough on the form. Tap the mold lightly on the work surface to remove air bubbles.Place a round stand (cake stand, basket steamer, removable cake pan rim, or 2-inch-high empty cans with the ends cut out) in a 12-to 14-inch steamer, 14-inch wok, or 12-inch skillet (with sides at least 2 inches high; the steamer should be wide enough to allow the sides of the mold for the cake, they didn't touch). Pour water into the steamer about 1/2 inch below the top of the stand. Cover the steamer and bring the water to a boil over high heat.Place the pie on a wire rack and cover the steamer (if the pie is uncovered, cover the steamer with a large piece of foil, covering it tightly around the edges so that no steam escapes); reduce the heat to medium and steam until a toothpick inserted in the middle of the pie comes out clean, 20 to 25 minutes. If necessary, add more boiling water to maintain the level. Quickly and carefully remove the lid so that condensed steam does not get on the cake. Remove the sponge cake from the steamer.Swipe the knife between the sponge cake and the edge of the mold to loosen the edges. Flip onto a wire rack, remove the pan and parchment, and flip again onto another wire rack. Let the cake cool for at least 10 minutes. With a serrated knife, cut the sponge cake into lozenges or slices. Serve warm or chilled.