Preheat your oven to 170°C (340°F). Prepare an 8-inch aluminum chiffon cake tin with a removable base, ensuring the tin is left ungreased to achieve the desired texture.

In a medium bowl, whisk together the egg yolks, whole milk, vegetable oil, caster sugar (I), and vanilla extract until smooth and well-combined. Sift in the cake flour and baking powder, gently mixing until no lumps remain. Be careful not to overmix.

In a separate large mixing bowl or the bowl of a stand mixer, beat the egg whites until they become foamy. Gradually add the caster sugar (II), a little at a time, while whisking on medium speed. Continue whisking until the egg whites form stiff peaks, ensuring the meringue holds its shape.

Carefully fold a third of the meringue into the egg yolk mixture to lighten it. Once incorporated, gently transfer this mixture into the remaining meringue. Using a spatula, fold the two mixtures together with light, sweeping motions, taking care not to deflate the batter.

Pour the batter into the prepared cake tin, smoothing the surface with a spatula. Gently tap the tin on the countertop a few times to release any large air bubbles trapped within the batter.

Bake the cake for approximately 45 minutes, or until a skewer inserted into the center comes out clean. Once baked, immediately invert the tin onto a wire rack to cool. Allow the cake to cool completely in the tin to prevent it from collapsing.

Once the cake is fully cooled, run a thin knife around the edges of the tin and the base to release it. Serve as desired, enjoying its soft, airy texture.