Line the base of an 8-inch/20-cm round cake pan with parchment. Make sure the pan fits comfortably in the steamer and leaves enough room above it for the cake to rise.

Bring the steamer water to a full boil before adding the batter. Wrap the lid with a clean towel or plan to cover the cake pan loosely with foil so condensation does not drip onto the cake.

Sift the flour, baking powder, and salt together. In a separate bowl, mix the milk, neutral oil, and vanilla extract.

Beat the room-temperature eggs and sugar on medium-high speed for 6–8 minutes, until very pale, thick, and able to hold a ribbon when the whisk is lifted. This whipped mixture provides most of the cake’s lift.

Fold the sifted dry ingredients into the egg mixture in two or three additions. Use a gentle motion and stop as soon as the flour disappears to protect the air bubbles.

Stir a small amount of the batter into the milk-and-oil mixture until smooth. Fold that loosened mixture back into the main batter gently and evenly so the oil does not sink and collapse the foam.

Pour the batter into the prepared pan and tap the pan lightly once or twice on the counter to release large air bubbles. Place it in the fully boiling steamer and cover with the towel-wrapped lid or loose foil.

Steam over medium-high heat for 30–35 minutes, keeping the lid closed during the first 25 minutes. Test the center with a skewer; the cake is ready when the skewer comes out clean.

Remove the pan from the steamer and let the cake cool for about 10 minutes. Run a thin knife around the edge if needed, then unmold, remove the parchment, slice, and serve.