Place half the custard, the rum, sugar, vanilla and spices in a medium saucepan. bring to the boil, whicking until sugar dissolves. Simmer for 2 minutes; remove from heat.

Place gelatine leaves in a bowl of cold water. Stand for 5 minutes or until softened. Squeeze excess water from gelatine, add to hot custard mixture; stir until dissolved. Transfer mixture to a large heatproof bowl; whisk in remaining custard. Stand for 5 minutes or until cool.

Grease a deep 15cm round cake pan; line base and side with two layers of baking paper, extending the paper 5cm above the edge of the pan. Cut each cake in half; reserve trimmings until required. Place one cake layer in the base of the pan.

Beat cream in a medium bowl with an electric mixer until medium peaks form. Fold whipped cream and custard together. Working quickly, pour one cup of custard cream over cake in pan; top with another cake layer. Repeat layering with remaining cake layers and custard cream, finishing with custard cream over the top. Use a small palette knife to level surface. Tap pan on the bench to remove air bubbles. COver; refrigerate for at least 4 hours.

Meanwhile make rum butterscotch sauce

Place skewers on an oven tray lined with baking paper. Place chocolate in a paper piping bag. Snip off the end of piping bag with scissors. Pipe tree shapes halfway up the skewers; decorate with sprinkles or cachous. Freeze chocolate until firm.

Remove cake carefully from pan. Insert trees into cake; crumble some of the reserved cake trimmings around the tree trunks. Serve cake with rum butterscotch sauce.

Combine ingredients in a small heavy-based saucepan. Bring to the boil, stirring, until sugar dissolves. Simmer for 5 minutes or until sauce thickens. Cool; refrigerate until cold and thick.