Preheat oven to 350 degrees Fahrenheit. Afterward, grease and line the Bundt pan with parchment paper.
Then whisk the flour, baking soda, baking powder and salt in a large bowl.
After that, in a saucepan heated on medium heat, stir in the butter and ginger beer until the butter dissolves, then remove the saucepan from the heat.
Afterward, place the unsweetened cocoa and sugar in the saucepan and stir until well mixed.
Then gradually pour in the rum and mix thoroughly. After that, carefully add the eggs one at a time; make sure to stir in before adding another egg.
Next add place buttermilk and vanilla, stir to combine and mix in the flour mixture. Whisk until completely incorporated.
Afterward, pour the cake batter into the prepared Bundt pan and bake in the oven for 50- 55 minutes, or you can insert a skewer in the center. If it comes out clean, then it is done.
Finally, remove from the oven and place the Bundt pan on a wire rack to cool completely.