In a large mixing bowl, combine currants, sultanas, raisins, mixed peel, and glacé cherries. Pour in dark rum or sherry, ensuring all fruits are well coated. Cover the bowl and let the mixture soak for several hours or ideally overnight.

Preheat your oven to 325°F (165°C) and prepare an 8 to 10-inch deep round cake pan by lining it with parchment paper.

Sift together plain flour, cocoa (if using), salt, baking powder, and mixed spice in a separate bowl.

Beat softened butter and soft brown sugar together until light and fluffy, then gradually add in the eggs.

Gently fold the sifted dry ingredients into the creamed mixture, then add soaked fruit and nuts, mixing thoroughly.

Pour batter into the prepared cake pan and bake at 325°F (165°C) for 45 minutes, then reduce temperature to 300°F (150°C) for an additional 40 to 60 minutes.

Let the cake cool in the pan for at least one hour before transferring to a wire rack to cool completely.

Wrap the cooled cake tightly in aluminum foil and store in a cool, dry place. Feed the cake weekly with dark rum.

Before serving, unwrap the cake and cover with marzipan and royal icing.