- Sprinkle the powdered gelatin over the cream. Let sit for a few minutes to bloom the gelatin.
- Combine egg yolk, castor sugar, and milk. Cook on a low flame for about 10 minutes.
- Add the cream/gelatin mixture and instant coffee powder. Mix well until thoroughly combined and there are no lumps of gelatin. Cool slightly.
- Whip the egg whites in a bowl till they are fluffy. Fold the whipped whites into the egg yolk custard mix.
- Transfer mousse mixture to serving dish(es). Refrigerate for an hour.
- Combine the heavy cream, vanilla, and sugar. Whip to medium peaks.
- Serve the mousse with the whipped cream, and garnish with grated chocolate.