1. Preheat the oven to 200°C (392°F).
2. Separate the egg whites from the yolks, then beat the egg whites until they become frothy.
3. Add the sugar and continue beating until you obtain a meringue-like batter.
4. Add the egg yolks and beat for a few more moments.
5. Incorporate the orange blossom water.
6. Then gently fold in the cornstarch using a spatula.
7. Prepare the base of the rolled cake by spreading the batter on a baking sheet lined with parchment paper, to a thickness of about 1 cm.
8. Place the baking sheet in the oven at 200°C (392°F) for 6 to 8 minutes.
9. For the chocolate mousse:
Melt the chocolate and butter together in a double boiler.
10. When it is smooth, add the egg yolks off the heat.
11. Beat the egg whites until stiff peaks form.
12. Pour the melted chocolate over the egg whites and gently fold together to avoid deflating the mixture.
13. For assembly:
Fill the genoise cake with the chocolate mousse, no specific technique required.
14. Cover with more chocolate mousse and sprinkle with praline.
15. Refrigerate overnight and it will be ready for the next day!