Slice the stick of butter lengthwise twice, rotate the stick and slice lengthwise twice more. looking at the end you should have 9 relatively equal size squares. Now slice the butter crosswise so as to make small cubes of butter. Add these to the dry ingredients and mix thoroughly. These cubes of butter should not mix in but spread evenly throughout the mixture.
Place the remaining ingredients, the rum, oil, milk, eggs and vanilla in a large meauring cup or small bowl. Pour the liquid ingredients into the dry while mixing on slow speed. Gradually increase the speed and mix well for a couple minutes. Pour mixture into your pan, do not use spatula or other device to spread. Allow batter flow evenly on its own.
Place in oven and bake for 60 minutes Approximately 10 minutes before the cake is finished, place 1/2 cup butter, 1/2 cup water, and 1 cup sugar in a sauce pan over medium heat. Stir constantly until the sugar is dissolved. Allow to boil for a few minutes until it has thickened slightly.
It should resemble a syrup. Allow to cool for about 10 minutes then stir in the Rum and Vanilla. Adding the rum too soon will cook off the alcohol At this point the cake should have been out of the oven for about 10 minutes. Now slowly pour your rum sauce over your cake.
It will pool around the edges but thats OK, it will absorb quickly. After about 5 minutes or once all the Rum has soaked in, invert your Bundt Pan over a plate. The cake should slide out easily.