- With the rack in the middle position, preheat the oven to 150°C (300°F). Line two 13 x 23-cm (5 x 9-inch) loaf pans or three 10 x 18-cm (4 x 7-inch) baking pans with parchment paper. Let the paper overhang 2 sides to make it easier to unmould the cakes. Butter the other 2 sides.
- In a bowl, combine the flour, spices, baking soda, baking powder and salt. Set aside.
- In another bowl, cream the butter and brown sugar using an electric mixer. Add the eggs one at a time, beating until the mixture is smooth. Set the mixer to low speed and add the flour, alternating with the rum and molasses. Transfer the batter to a large bowl and add the remaining ingredients. Mix well, stirring with a spatula or wooden spoon for 4 or 5 minutes. Scrape the batter into the pans. Bake until a toothpick inserted in the centre comes out clean, about 90 minutes for smaller cakes or 2 hours for larger cakes.
- Remove the fruitcakes from the oven and drizzle with rum if desired. Cover with aluminum foil and let rest on a cooling rack for 10 to 12 hours. Unmould.
- Serve thinly sliced.