Preheat oven to 350º
Melt butter and set aside.
Beat egg. Set aside.
Add Guinness, molasses, vanilla, and guava jam, and egg to a large bowl.
Add sugar and stir until it's completely mixed in and sugar has dissolved.
Blend plantain in a food processor until mashed well.
Add plantain, zests, and ginger to Guinness mixture and set aside.
In a separate bowl, mix flour, salt, baking powder, and spices until well combined.
Add raisins and golden raisins.
Add wet ingredients to dry ingredients.
Spoon batter into a prepared loaf pan.
Bake loaf for 1 hour 15 minutes or until a wooden toothpick comes out clean.
Let set for 10 -15 minutes in pan until cool enough to handle.
Move to a wire rack to completely cool.