Chocolate Layered Mousse

Dark Chocolate Mousse:
Melt the chocolate and butter together in a medium bowl placed in a pan of barely simmering water. Or melt in a microwave oven on medium heat for about 1 1/2 minutes. Stir from time to time to hasten melting. When melted and smooth, whick in the dissolved coffee powder and egg yolks. Remove from heat and set aside.
In a clean and dry mixing bowl, beat the egg whites and cream of tartar at medium speed until soft peaks form. Gradually sprinkle in the sugar, beating at high spead until stiff but not dry. Fold 1/4 of the egg whites into the chocolate mixture to lighten it. Fold the remaining egg whites into the mixture until completely incorporated. Pipe the mousse into serving cups and refrigerate for at least 2 hours to set.
White Chocolate Mousse:
Soak the gelatine in cold water until soft, then drain and squeeze out excess water.
Pour 125 ml of the cream into a sauce pan and bring to a boil. Remove from the heat. Add the gelatine and stir until smooth. Place the white chocolate in a heat proof bowl and pour the cream over this. Stand for 30 seconds and slowly stir until amalgamated. Allow to cool.
In another bowl, whip the cream until soft peaks form and fold into the cooled white chocolate mixture. Remove the glass from the refrigerator and top with the white chocolate and allow to set.
Top with a layer of Nutella