Oil and line a 1-litre loaf tin with cling film. Put the coffee, Tia Maria or brandy, egg yolks and sugar in a bowl and stir to dissolve the coffee. Put the egg whites in a large bowl and pour the cream in another.
Beat the egg whites until stiff with an electric whisk, then quickly beat the egg yolk mixture until thick and leaving a trail. Now beat the cream until it holds its shape. If you beat everything in this order, you don’t need to wash the whisks in between.
Fold the cream into the coffee mixture, then carefully fold in the whites. Fold through the Toblerone and tip into the loaf tin. Lightly cover the surface with cling film. When frozen, overwrap in foil and freeze. Will keep for up to 6 weeks. You can make the chocolate curls (see video link, above, for instructions) and keep them in a airtight container or freeze.
To serve, unwrap and turn onto a platter. Strip off the cling film and serve topped with the chocolate curls.