Preheat the oven to 350°F (175°C). Grease and line a loaf pan with parchment paper, ensuring there’s enough room for the dough to rise.
Prepare the dry ingredients: In a large mixing bowl, sift together the all-purpose flour, baking powder, cinnamon, nutmeg, cloves, and allspice. Set aside.
Cream the butter and sugar: In another mixing bowl, cream together the softened butter and brown sugar using a whisk or electric mixer until light and fluffy, about 3-4 minutes.
Add the eggs and vanilla: Beat in the eggs one at a time, mixing well after each addition. Stir in the vanilla extract and optional citrus zest (orange or lemon).
Combine the wet and dry ingredients: Gradually add the dry ingredients to the wet mixture, alternating with the milk. Mix gently until just combined.
Fold in the dried fruits and nuts: Carefully fold in the mixed dried fruits, nuts, and rum/brandy (if using). The mixture should be thick and sticky.
Transfer to the pan and bake: Pour the batter into the prepared loaf pan, smoothing the top with a spatula. Bake for 50-60 minutes, or until a toothpick inserted into the center comes out clean.
Cool and serve: Allow the bun to cool in the pan for 10 minutes before transferring it to a cooling rack to cool completely. Slice and enjoy!