Preheat the oven to 170°C. Line the bottom of the cake pan with parchment paper, but do not grease the sides. The batter needs to rise up the sides of the pan to reach its full height. If you like, line the sides with parchment paper as well.
Whisk together the white rice flour and cornstarch in a small bowl, then sift the mixture at least twice.
Beat the eggs, sugar, salt, and vanilla extract in a large bowl using a hand mixer or stand mixer on high speed for 4 to 5 minutes, until the mixture is pale, thick, and tripled in volume.
Sift the flour and cornstarch mixture over the whipped eggs in three additions. Gently fold after each addition until no white streaks remain, taking care not to deflate the mixture.
Transfer a small amount of batter to a small bowl and stir in the sunflower oil until smooth. Gently fold this mixture back into the batter.
Pour the batter into the prepared pan and bake for 40 to 45 minutes. The cake is done when the top is golden and springs back lightly to the touch.
Remove the cake from the oven and immediately run a thin knife around the edge. Invert it onto a wire rack and let it cool completely.