Melt the chocolate and butter in a bowl placed over a pot of barely simmering water, stirring gently until melted. Remove from the heat and allow to cool.
Whip the cream to soft peaks and stir in the coffee powder and chill.
In a clean bowl, whip the egg whites until foamy, then gradually add the sugar while continuing to whip the whites until they hold a soft peak.
Fold the whipped cream quickly into the chocolate in two batches, then fold in the meringue all at once.
Pour the chocolate mixture in the serving dish over the crushed chocolate cookie sandwiches and chill about for 2 hours then top with chocolate shavings and some Halloween decoration.