In a small bowl, mix the gelatin with water and let it bloom for 5 minutes.

In a saucepan, warm up 1/2 cup of heavy cream and add the bloomed gelatin, stirring until dissolved.

Pour the mixture over the chopped chocolate and stir until smooth. If using, add instant coffee.

In a separate bowl, whip the remaining cream to soft peaks and gently fold into the chocolate mixture.

Pour half of the mousse into a springform pan lined with crushed cookies and refrigerate.

For the vanilla mousse, warm milk and stir in sugar and vanilla extract.

Gently fold in whipped cream into the mixture and layer on top of the chocolate mousse.

Refrigerate for at least 4 hours or until set. Serve chilled.