Preheat your oven to 350°F (175°C).
Grease and flour a bundt cake pan.
In a mixing bowl, cream together the butter and sugar until fluffy.
Add the eggs one at a time, mixing well after each addition.
Stir in the dark rum and vanilla extract.
In a separate bowl, combine the flour, baking powder, and salt.
Gradually add the dry ingredients to the wet mixture, alternating with milk.
Fold in the chopped nuts if using.
Pour the batter into the prepared bundt pan.
Bake for 50 minutes or until a toothpick comes out clean.
Let the cake cool for 10 minutes before inverting onto a serving plate.