Preheat the oven to 160°C/325°F.
Cream the butter and sugar at high speed in a stand mixture until it’s fluffy and looks white, 5-7 minutes.
Add in your oil and beat until well incorporated.
Stir in the eggs, one at a time, beating the mixture well between each one.
In a bowl, mix flour, baking powder, and salt.
Whisk ⅓ of the dry ingredients into the wet, followed by ½ of the buttermilk. Then, whisk in another ⅓ of the dry into the wet, followed by the rest of the buttermilk. Then add the last of the dry ingredients and mix until just combined.
Using a spatula, gently fold in the rum and vanilla extract.
Stir well until everything is thoroughly combined. Scrape down the sides of the mixing bowl.
Pour batter into a well-greased 10-inch-bottomed tube pan or bundt pan.
Bake at 325℉ (160℃) until a tester inserted into the center comes out clean, 55-60 minutes. Remove from the oven.
Transfer the pan to a wire rack and cool for at least 15 minutes. Then, carefully invert the pan to release the cake. If it appears to be stuck, gently tap on the sides of the pan to help release the cake.