Preheat oven to 325F. Grease a 10 or 12-cup bundt pan and dust with Oreo cookie crumbs or cocoa powder.
In a medium bowl, whisk together flour, cocoa powders, baking soda, and salt. Set aside.
In a measuring cup, mix milk and sour cream until combined. Set aside.
Place butter and sugar into the bowl of an electric mixer fitted with the paddle attachment. Beat on med-high until light and fluffy (approx 3mins).
Add eggs one at a time, fully incorporating after each addition. Add vanilla.
Reduce speed to low. Add flour mixture in 2 batches, alternating with milk/sour cream mixture. Beat until just combined.
Fold in Oreo cookie chunks.
Spread the batter evenly in the bundt pan.
Bake for approx. 55mins or until a cake tester comes out clean.
Cool in bundt pan for 10mins. Rap bundt pan on the counter to loosen cake and turn out onto cooling rack to cool completely.