Preheat the oven to 350°F. Place cupcake holders in a cupcake pan (this recipe makes 24 cupcakes).
In a medium bowl add the flour, baking soda and salt and whisk together until combined. Set aside.
Add the butter, sugar, brown sugar and rum to the bowl of a stand up mixer with the paddle attachment. Beat 2-3 minutes on medium speed until the butter is light and fluffy. Pour in the oil and eggs and beat until combined.
On low speed, alternate adding the dry mix and buttermilk to the mixing bowl until combined. Add the coconut so it mixes throughout.
Pour the batter into the cupcake pan, ⅔ full. Bake at 350° for 15-17 minutes until the tops are golden brown and a tookpick comes out of the middle clean. Let them cool completely on a cooling rack.