Pre-heat oven to 350 degrees. Using a pastry brush, generously brush the inside of a Bundt pan with super soft butter. In a small bowl, mix together a couple teaspoons of each all-purpose flour and cocoa powder. Dust the inside of the pan with the cocoa/flour mixer and tap our the excess. Set aside the pan.
In a large bowl, sift together the flour, baking powder, salt, and baking soda. Add the brown and white sugars and set aside.
In a medium-large saucepan, melt together the coffee, cocoa powder, butter, and dark chocolate. Whisk until melted and combined. Remove from the heat.
Whisk together the sour cream, buttermilk, oil, vanilla, eggs, and egg yolks. Pour the egg mixture into the chocolate mixture and whisk to combine. In two batched, carefully stir in the dry ingredients into the chocolate mixture. Stir until smooth.
Pour the cake batter into the prepared pan.
Bake in the pre-heated oven for 45 to 50 minutes, or until a wooden skewer inserted into the center of the cake comes out clean.
Allow the cake to cool for about 10 to 15 minutes (it should still be warm). Place a cutting board or cooling rack on top of the pan. Using oven mitts, carefully flip the cake pan and cutting board upside-down to untold the cake. Continue to cool completely before adding the glaze.