Set your oven to 325 degrees Fahrenheit to preheat.
Apply nonstick cooking spray to a large 12-cup Bundt pan.
Spread the chopped walnuts evenly on the bottom.
In a large bowl, combine Cake Mix, oil, pudding mix, eggs, milk, vanilla extract and rum. Mix on medium speed with an electric mixer for 2 to 3 minutes, stopping to scrape down the bowl halfway through.
The batter should have a very smooth consistency. Pour the mixture into the Bundt pan.
Bake the cake for approximately 55 minutes, or until it turns fully golden and a tester comes out clean. Additionally, the cake should spring back when touched.
Take the cake out of the oven and put it on a cooling rack while you prepare the soaking glaze.