Step 1: Begin by soaking the fruits. In a large bowl, combine the currants, sultanas, raisins, glacé cherries, mixed peel, and chopped almonds. Pour 150ml of brandy over the fruit, stir well, cover, and let it steep for at least 24 hours, or preferably a few days, stirring occasionally. This plumps the fruit and infuses it with flavor.
Step 2: Preheat your oven to 140°C (120°C fan/Gas Mark 1). Grease an 8-inch (20cm) round cake tin and line it with a double layer of baking parchment. Ensure the parchment comes about 2 inches higher than the tin's rim to protect the cake from burning.
Step 3: Sift the plain flour, baking powder, salt, mixed spice, ground cinnamon, and ground nutmeg into a medium bowl. Set aside.
Step 4: In a large mixing bowl, cream together the softened butter and dark muscovado sugar until light and fluffy. This can take several minutes with an electric mixer.
Step 5: Gradually add the lightly beaten eggs to the creamed mixture, a little at a time, beating well after each addition to prevent curdling. If the mixture starts to curdle, add a spoonful of the sifted flour.
Step 6: Stir in the black treacle, orange zest, and lemon zest until well combined.
Step 7: Gently fold in the sifted dry ingredients until just incorporated. Be careful not to overmix.
Step 8: Add the soaked fruit mixture (along with any remaining brandy liquid) to the cake batter. Mix thoroughly until the fruit is evenly distributed throughout the batter.
Step 9: Spoon the batter into the prepared cake tin, smoothing the top. Make a slight hollow in the center to help the cake rise evenly.
Step 10: Bake in the preheated oven for approximately 3 hours 30 minutes, or until a skewer inserted into the center comes out clean. If the top starts to brown too quickly, cover it loosely with foil.
Step 11: Once baked, remove the cake from the oven. While still warm, pierce the top of the cake with a skewer and spoon 1-2 tablespoons of additional brandy over it. Let the cake cool completely in the tin.
Step 12: Once cold, remove the cake from the tin. Pierce the top and sides again with a skewer and spoon over more brandy (about 1-2 tablespoons). Wrap the cake tightly in a double layer of baking parchment, then in foil. Store in an airtight container in a cool, dark place. Feed the cake with 1-2 tablespoons of brandy weekly (or every two weeks) until about a week before Christmas. Re-wrap securely each time.
Step 13: About a week before serving, you can decorate the cake with a layer of marzipan, followed by royal icing or fondant icing, as desired.