Soak the fruits: A day before (or at least a few hours), soak the mixed dried fruits in rum.
Prepare the oven: Preheat your oven to 160°C (320°F). Grease and line an 8-inch round cake pan.
Mix dry ingredients: In a bowl, whisk together the flour, baking powder, salt, and mixed spice powder.
Cream butter and sugar: In a large bowl, beat the softened butter and brown sugar until light and fluffy.
Add eggs: Beat in the eggs one at a time, mixing well after each addition.
Combine mixtures: Gently fold the flour mixture into the butter mixture. Do not overmix.
Add fruits and nuts: Fold in the rum-soaked fruits (along with any remaining liquid) and the chopped nuts.
Bake: Pour the batter into the prepared cake pan and level the top. Bake for about 1.5 to 2 hours, or until a skewer inserted into the center comes out clean.
Cool and store: Let the cake cool in the pan for 30 minutes before transferring it to a wire rack to cool completely. The cake can be "fed" with more rum over a few weeks for a richer flavor.