Whisk together the flour, dark cocoa powder, baking powder and salt.
Beat together the butter and oil. Then add the granulated sugar and beat until combined. Add the eggs one at a time, then add the vanilla extract.
Add half of the dry ingredients to the wet ingredients. Then add half of the milk, coffee, and yogurt and mix. Repeat with the other halves. Separate the cake batter into two 6 inch pans and bake for 35 minutes.
Beat the butter on high speed for 5 minutes. Add the powdered sugar, dark cocoa powder, salt, and milk/heavy cream until combined.
Once the cakes are cool, level them off using a cake leveler or serrated knife if they have a dome shaped topped. Frost and enjoy!