Prep the pan and oven: Preheat oven to 350°F (175°C). Generously coat a 10–12 cup Bundt pan with baking spray, or butter it well and dust with cocoa powder.
Mix the batter: In a large bowl, whisk cake mix and pudding mix to break up lumps. Add eggs, sour cream, oil, milk, and vanilla.
Beat on medium speed for 2 minutes until smooth and thick.
Fold in chips: Stir in chocolate chips with a spatula so they’re evenly distributed.
Fill the pan: Pour batter into the prepared Bundt pan and smooth the top. Tap the pan gently on the counter to pop any air bubbles.
Bake: Bake 40–50 minutes, until a toothpick inserted near the center comes out with a few moist crumbs. If the top is browning too fast, tent loosely with foil for the last 10 minutes.
Cool properly: Let the cake cool in the pan for 10–15 minutes.
Turn out onto a wire rack and cool completely before glazing or slicing.
Glaze (optional): Whisk powdered sugar, cocoa, milk, and a pinch of salt until smooth and pourable. Drizzle over the cooled cake.
Serve: Slice with a serrated knife for clean cuts. Enjoy at room temperature or slightly warmed.