Roughly chop the prunes.
Blend the dried fruit with a portion of the rum and sherry to a thick, chunky paste.
Blend until it is a thick but smooth consistency (with a little chunkiness).
Pour the entire mixture into a large bowl.
Pour the mixture into a large jar, add the remaining alcohol, seal the jar, and store it for at least 1 month.
Preheat the oven to 250°F (120 °C). Grease and line baking pans with parchment.
Cream butter and sugar until pale. Beat in eggs one at a time, then add vanilla, mixed essence, lime zest, and bitters.
Beat in eggs one at a time, then add vanilla, mixed essence, lime zest, and bitters.
Fold in half of the soaked fruit, then half of the dry mixture (flour, spices, baking powder, salt).
Repeat.
Add browning and mix to combine.
Divide into prepared pans (fill 2/3 full). Bake for 2 1/2 hours or until a toothpick inserted comes out clean.
Brush the cake tops with a mix of rum and sherry.
Cool completely, then brush again before wrapping and storing.