Preheat the oven to 180°C/160℃ fan/350°F/gas mark 4. Grease a 23 x 33 cm/9 x 13 in rectangular cake tin and line with baking parchment.
Whisk together the golden syrup, brown sugar, milk, vinegar and melted butter in a large bowl until fully combined.
Whisk in the baking powder and soda, espresso powder, cocoa powder and spices, followed by the plain flour. Be careful not to over-beat the batter.
Pour the batter into the prepared tin and spread it level. Bake for about 25 minutes until a skewer inserted into the centre comes out clean. Start checking for doneness after 20 minutes, you do not want to overbake the cake or it may be dry. Leave the cake to cool in the tin completely.
Once the cake has cooled completely, trim off the edges and cut it widthways into 3 equal pieces, use a ruler for accuracy. Trim off the tops of the cakes to level them so they are completely flat.
Roll the marzipan out into a rectangle and trim the edges so that it is exactly the same size as the cake pieces. Spread a very thin layer of jam over one of the cake layers, avoid using any pieces of fruit. Place the marzipan on top of the jam covered cake, spread another thin layer of jam on top of the marzipan, again with no pieces of fruit, and place another cake layer on top.
Spread a thick layer of jam on top of the cake, including the fruit pieces this time, and place the final cake layer on top.
Melt the chocolate and coconut oil together, either in short bursts in the microwave, or in a bain marie, then pour it over the top of the cake. Use the back of a spoon to encourage it to drip down the sides.
If you want to decorate the cake with chopped nuts, do so before the chocolate sets. Allow the chocolate to set before serving the cake. Store in a covered container in the fridge for up to 5 days.