Preheat over to 350 F
Sieve all the dry ingredients, except the granulated sugar, into a large bowl and mix.
In a smaller bowl, mix in the milk and vinegar and let it stand for 1 to 2 minutes to turn into buttermilk.
Now add in the granulated sugar and whisk till all the sugar dissolves.
Now add in the oil and vanilla extract to the buttermilk mix and stir again.
Add wet ingredients into the dry ingredients and mix till everything is evenly combined and no lumps are seen. Do not overmix.
Add in 4 tablespoons rum and mix again.
Grease a 9 inch bundt cake mold (or line a 9 inch cake pan with parchment paper and grease it).
Pour batter into it. Gently tap the mold on a table top to remove air bubbles.
Place in the oven for 30 to 40 minutes. Starting at 30 minutes, check if the cake is done by inserting a skewer and see if it comes out clean.
Once baked, let it cool in the pan for 30 min. Then remove from the cake mold and let it cool to room temperature on a wire rack.