Bloom the gelatin in 50 ml of cold water, ideally in a saucepan, for 10 minutes until it swells.

In a mixer bowl, combine the sour cream and cream and whip until thick and increased in volume.

Sift in the powdered sugar and cocoa and whip again until thick.

Melt the gelatin and pour it into the mousse in a thin stream, whip for another minute. The mixture will become less thick - that's normal.

Pour the mousse into cups or molds and refrigerate or freeze until fully set.

Grate chocolate on top before serving. Enjoy!