Make a filling by combing 2 tablespoons Butter cake mix with ½ cup chopped pecans, 1 tablespoon cinnamon, and 2 tablespoons sugar. Set mix aside.
Mix together the rest of the cake mix with the sour cream, ¼ cup water, eggs, rum, and vanilla.
Pour ½ of the mixture into a bundt pan that has been prepped with a bit of oil and flour. Sprinkle with ¾ of the filling. Pour the rest of the batter on top. Sprinkle with the rest of the filling.
Cook at 350° for 40 minutes to an hour.
Remove the cake from the oven and let it cool for 5 minutes. Remove the cake from the pan and place it on a plate. Now randomly poke holes with a toothpick on the top bottom and sides of the cake. Next, return the cake to the bundt pan.
Combine butter, sugar, ¼ cup water in a saucepan. Heat until the sugar dissolves. Remove from the heat and add the rum. Pour onto the cake. Allow it to soak until it all kind of dissolves. Move cake to serving platter and allow it to cool.
While cake cools, cream confectioners’ sugar and butter until blended. Add vanilla. Add milk tablespoon by tablespoon until you get a smooth consistency.
Spoon onto the cake and allow it to cascade down the cake.