Place the mixed dried fruits, alcohol, butter, brown sugar, treacle, milk, vinegar, vanilla extract and orange zest in a large saucepan. Heat gently, stirring often, until the butter has melted then bring to the boil. Remove from the heat and set aside to cool to warm room temperature, about 1 hour.
While the mixture is cooling, preheat the oven to 140°C/120°C fan/275°F/gas mark 1. Grease a deep 20 cm/8 inch round cake tin and line it with a double layer of baking parchment.
Add the ground almonds to the cooled fruit mixture and sift in the flour, cocoa powder, baking powder, bicarbonate of soda, mixed spice and cinnamon. Stir with a spatula to form a batter with no dry patches.
Add the chocolate chips and gently stir in.
Scrape the batter into the prepared tin and use a spatula to spread it level. Because it is so thick it doesn't spread much in the oven so it is important that you get it as even as you can.
Bake for 2 ½ to 3 hours, until firm to the touch and a skewer inserted into the centre (avoiding any chocolate chips) comes out clean or with a few moist crumbs but no wet batter. (My cake took 2 ¾ hours to bake).
Allow the cake to cool for 30 minutes then brush with 1 Tablespoon of your preferred alcohol. Leave to cool in the tin completely (about 8 hours).
Once the cake is completely cold, remove it from the tin and brush all over with a little alcohol.
Wrap the cake up in baking parchment then tin foil (it MUST be completely cold first), and store in an airtight container, feeding every week or two with alcohol, for up to three months.