This cake contains no raising agents: the light airy texture relies on the air beaten into eggs. As the air expands in the heated oven, the cake rises. So you have to beat for a long time your mixture of eggs and sugar: remember, don't get tired to beat!
Prepare and butter the cake tin. Preheat oven to 180°C (350°F).
Meanwhile whisk the eggs, sugar and the vanilla powder to the ribbon stage. In other words: when you lift the whisk out of the bowl, the mixture should fall, leaving a "ribbon-like" trail on the surface of the mixture.
Put the flour and salt in a colander and sift it on the mixture as gently as possible, stirring with a wooden spoon.
Pour the mixture into the tin and bake about 30 minutes, until center springs back when touched lightly with a fingertip. Don't open the oven during cooking time.
Let the cake cool in the oven.