In a bowl, combine the warm water, yeast, and sugar. Lightly stir the mixture just enough to dissolve the sugar and yeast.
In another bowl, combine the flour and the yeast mixture and whisk for about two minutes, just enough to mix the gluten.
Gradually add the butter and continue mixing the batter for a few more minutes, until the butter is well-combined with the batter. Set aside.
Drain the raisins, but make sure to set aside the rum since you’ll be using it later.
Add the raisins to the batter. Fold in the raisins to combine it well with the batter.
Prepare the mold (or molds, depending on the size) by brushing it with melted butter.
Pour the batter into the mold. Make sure to only fill it halfway. Let it rise for about 20 minutes in a warm area.
Once it's doubled in size, bake it for 15 to 20 minutes in the preheated oven. Note: Halfway through baking, turn the cake around to even out the cooking, in case the oven doesn’t heat up evenly.
Once it turns golden brown, or when it is dry enough that it easily comes out of the mold, it is done. Set it on a cooling rack.
Notes
Soak the raisins in the rum for 4 hours beforehand. Make sure they are more than covered in it. Set aside.