Preheat the oven to 350 degrees Fahrenheit. Line an 8-inch circular cake pan with parchment paper, or grease the cake pan with butter, then lightly coat the pan with flour.
Add half of the sugar to the egg whites, and beat the egg whites until they are stiff and glossy.
In a medium bowl whisk the egg yolks with the remaining sugar until thick and pale yellow.Add the orange juice and vanilla.Whisk to mix. Add the sifted flour and cornstarch and whisk until smooth.
Add ⅓ of the egg whites into the batter and gently mix it in to the egg yolk mixture. Add the second third of the egg whites and fold until no egg whites remain. Repeat with the last addition of egg whites.Pour in the melted butter and fold to incorporate.
Pour the cake batter into the prepared cake pan andbake the for 25 to 30 minutes. Insert a thin skewer or toothpick into the centers. If it comes out dry, the cake is done. Let the cake cool completely on a wire rack. Run a knife around the inside of the pan to loosen the cake, and remove.