Preheat the oven to 350℉. Lightly grease a bundt cake pan.: The moment you set the oven, you will begin to smell a faint warmth as it comes to temperature, and properly greasing the pan prevents sticking and helps the cake release cleanly. I often run a fingertip around the pan to ensure even coverage; if areas are missed the cake can cling and tear. A common error is not preheating long enough, causing the cake to bake unevenly.
In a large bowl, use an electric mixer to mix chocolate cake mix, pudding, eggs, water and oil until smooth. Use a rubber spatula to fold in sour cream and chips. Stir until the sour cream is incorporated.: As you beat these components, the batter will develop a satin sheen and a slightly thick, glossy texture, and the mixer will hum with steady rhythm. The scent shifts from dry cocoa to a wetter, deeper chocolate perfume. Folding in the sour cream and chocolate chips by hand preserves air that the mixer incorporated, creating an even, tender crumb. Overbeating here would deflate that air and tighten the cake texture, so stop once uniform.
Pour the batter into the prepared bundt pan and bake for 50 to 60 minutes, or until a toothpick inserted in the center of the cake comes out clean.: Once in the pan the batter sits low and glossy, and as it bakes the top will turn matte and slightly domed while the edges pull away from the pan. You will smell a deepened chocolate aroma and notice gentle, steady bubbling inside the oven. Using a toothpick checks doneness without overbaking; if crumbs cling the cake needs more time. Avoid opening the oven frequently, which can cause the center to sink.
Cool thoroughly before removing from pan. To remove, invert onto serving dish and tap firmly on pan. If necessary, gently run a plastic knife around the inner circle of the pan.: Cooling lets steam dissipate and the crumb stabilize, creating a clean release from the pan. The cake will stop sizzling and the surface will firm slightly; tapping the inverted pan produces a satisfying hollow sound when released. If you try to unmold too soon, the cake can fall apart, so patience pays off. Use a plastic knife only if you feel resistance, avoiding metal which can scratch the pan.
Sprinkle with powdered sugar just before serving for a nice presentation.: The final touch of powdered sugar brightens the deep chocolate and adds a whisper of sweetness, settling into nooks of the bundt fluting for an appealing contrast. Dust it moments before guests arrive so it remains fresh and white rather than absorbed into the cake surface. If powdered sugar is added too early in humid conditions, it can dissolve and lose its visual effect.
