Preheat oven to 180 C / Gas 4. Butter and flour a 450g (1 lb) loaf tin and reserve.
In a large bowl cream softened butter with sugar. Add egg yolks and mix, then stir in flour. In a separate bowl beat egg whites with a pinch of salt until stiff peaks form. Gently fold egg whites into egg yolk mixture, being careful not to break the peaks.
Pour mixture into prepared loaf tin and bake in preheated oven for 40 minutes or until a skewer inserted in the centre comes out clean. Let cake cool and unmould from loaf tin.
Cut cake into slices about 6cm thick, then cut each slice (save one) into thirds for the train cars. Cut remaining slice in half for the locomotive (see photo).
Decorate train with caramels (wheels), icing sugar (snow), liquorice twists (logs), miniatures for passengers, etc. Use your imagination and enjoy!