Preheat the oven to 170°C (338°F).
Whip the egg whites until foamy, then gradually add the sugar in two parts to make a meringue.
Add the egg yolks, milk, and low-fat cocoa powder and mix well.
Sift in cake flour and baking powder, then add to the mixture.
Fold the meringue into the batter in 2 to 3 parts.
Line a pan with parchment paper and pour in the batter.
Bake in the oven for 30–35 minutes.
Let cool on a wire rack.