Preheat the oven to 170°C (340°F).
Separate the egg yolks from the egg whites.
Add half of the sugar to the yolks and mix well.
Gradually add the remaining sugar to the egg whites and whip until stiff peaks form.
Sift cake flour into the yolk mixture and gently combine.
Fold the whipped egg whites into the yolk batter in batches, mixing gently.
Pour the batter into the mold and bake in the oven for 30 minutes.
Finish by spreading fresh cream on the cooled castella.