Preheat oven to 350F. Grease a 9-cup bundt pan.
In a medium bowl, whisk together flour, cocoa powder, baking soda, and salt. 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. Alternate adding flour mixture with Baileys and sour cream (3 additions of flour and 2 each of Baileys and sour cream). Beat until just combined.
Spread the batter evenly in the bundt pan.*
Bake for approx. 45-50mins or until a cake tester comes out clean.
Cool in bundt pan for 10mins. Whack bundt pan on the counter to loosen cake and turn out onto cooling rack to cool completely.