Preheat the oven to 350 degrees F.
Brush a 10 cup bundt pan with 1 tablespoon of melted butter and coat with cocoa powder.
In a large bowl, whisk together the cake flour, cocoa powders, baking powder, and salt. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter and sugar for 2-3 minutes until light & fluffy.
Mixing on low speed, add the eggs one a time.
Scrape down the bowl and mix in the vanilla.
Add half of the dry ingredients and mix until just combined.
Mix in the sour cream and oil.
Add the rest of the dry ingredients and mix until just combined.
Scrape down the bowl to ensure everything is evenly incorporated.
Pour the batter into the bundt pan and smooth out the top.
Tap the pan on the counter a few times to to release any air bubbles.
Bake the bundt cake for about 50-55 minutes or until a toothpick inserted comes out clean.
Allow the cake to cool in the pan for 10 minutes, then use a knife to loosen the cake from the sides. Turn the cake out onto a wire rack to cool completely.