1. Heat the oven to 180C / 160C fan / gas mark 4. Line your chosen tin(s) with baking parchment.
2. Put the dried fruit in a large mixing bowl and pour in100ml (3½ fl oz) of the herbal tea. Leave to soak for an hour, stirring occasionally.
3. Put the dates, remaining 200ml (7fl oz) of herbal tea and the mixed spice into a small saucepan and simmer gently together for 5 minutes. Take off the heat and leave to cool.
4. In a blender or food processor, puree the dates with the banana and 100ml (3½ fl oz) of the reserved liquid – remove this until smooth.
5. Transfer to a mixing bowl. Fold into the mixed dried fruit with the polenta and baking powder.
6. In a separate bowl, whisk the egg whites into soft peaks and fold into the fruit mixture using a large metal spoon. Spoon into the lined cake tins.
7. Bake for 45 minutes for individual cakes or 1hour -1½ hours for a large tin. Cover lightly with foil after 30 minutes. A skewer pushed into the centre of the cake should come out clean when it's cooked. Drizzle the brandy or sherry over the hot cake, if using, then leave to cool in the tins on a wire rack.
8. Decorate the top of the cake with a spiral of dried apple slices and some herbs and holly (see main picture) or dust very lightly with icing sugar through a festive stencil (see picture below).
- The cooked cakes keep well, wrapped in cling film and foil, in an airtight container for up to 3 days, or can be frozen.