Preheat oven to 180 degrees C.
Line a 18-20 cm spring form pan with a circle of baking paper and grease well inside the pan.
Sift flour, salt and cocoa powder and set aside.
In a large bowl beat egg yolks with sugar and vanilla until thick.
In another bowl beat the egg whites for about 5 minutes, until thick (wash and dry the beaters after the egg yolks).
Using a rubber spatula, gradually fold the dry ingredients to the egg yolk mixture, until combined. Carefully fold in the egg whites.
Pour the batter into the prepared pan and bake for 40-45 minutes or until a wooden skewer inserted in the center comes out clean. Remove the cake from the oven and let cool for few minutes. Transfer to a wire rack to cool completely.