Preheat oven to 350°F (175°C).

Grease a Bundt pan thoroughly.

In a large bowl, combine yellow cake mix, chocolate pudding mix, eggs, sour cream, oil, vanilla, and rum (if using).

Beat the mixture for 5 minutes. The batter will be stiff.

Stir in chocolate chips and chopped nuts.

Spoon the batter into the prepared Bundt pan.

Bake for 55 to 60 minutes, or until a wooden skewer inserted into the center comes out clean.

Let the cake cool in the pan for 10 minutes before inverting onto a wire rack to cool completely.