Cut cake into 10-12 slices. Place half the slices in trifle bowl. Sprinkle evenly with half of the Kahlua, top with half of the raspberries, sprinkle with 1/3 of the chocolate, spread with half of the custard. Repeat layers. Decorate with whipped cream, remaining dark chocolate and extra raspberries. Coffee Custard: Whisk egg yolks, cornstarch and sugar together in pan until smooth. Heat milk in separate pan, gradually stir into egg yolk mixture. Cook, stirring constantly until mixture boils and thickens. Add combined coffee, water and vanilla; cover surface with plastic wrap to prevent skin from forming, and cool to room temperature. Beat whipping cream until soft peaks form and fold into custard.