Preheat your oven to 350 degrees F. and grease a 10-inch bundt pan.
In a large bowl, combine the cake mix, instant pudding, eggs, vegetable oil, water, and sour cream. Mix until well combined but don't overmix.
Fold in the chocolate chips and then pour the batter into the greased bundt pan. Bake for 50-55 minutes.
Allow the cake to cool for 15 minutes before inverting the cake onto a plate.
To make the cream cheese frosting, cream the softened unsalted butter and cream cheese with an electric mixer until smooth and creamy. This should take about 1 minute.
Add the powdered sugar. Mix on low speed for about 20 seconds, then mix on high speed for 3-4 minutes or until the frosting is nice and fluffy.
Allow the cake to cool completely before frosting.
To frost the cake, position the bag just above the cake, close to the outer edge.
Squeeze and pull a line of frosting. Apply gentle pressure to the bag and slowly move it in a circular motion, following the curve of the cake. As you squeeze the frosting out, it will create a line that goes up and over the cake, into the center hole.