Preheat oven to 325 degrees Fahrenheit.
Grease and flour two 8" round (2" inch deep) cake pans and set aside.
In a small bowl, break up the sweet German chocolate and melt in the microwave. Set this aside to cool while you mix up the other cake ingredients.
In a large mixing bowl, whisk together the flour, cocoa powder, granulated sugar, brown sugar, baking soda, baking powder and salt.
In another bowl, mix together the buttermilk, regular milk, oil, eggs, and extract. Whisk well and set aside.
Make sure the butter is slightly cooler than room temperature. Add the butter (in chunks) slowly to your dry ingredients while mixing at medium-low speed. (You can turn your stand mixer on medium-low and leave it on while you add the butter chunks a bit at a time, or you can use a hand mixer.)
Turn the mixer up to medium and mix until all the flour is coated with the butter and the mixture is crumbly. It will have a sand-like texture.
Pour in about half of the liquid mixture. Mix on low to medium for about a minute.
Pour the last of the liquid mixture and mix again only until well combined. Don't over mix the batter at this point. Mixing it for several minutes is too long. Once all the ingredients are incorporated well, stop mixing.
Use a rubber spatula to scrape the sides and bottom of the bowl. Mix again for only about 10 seconds.
Add in the melted chocolate and mix again, until just combined.
Pour into prepared pans. The batter might look a bit grainy due to the brown sugar...that's okay.
Bake at 325 degrees for approximately 55-60 minutes. These layers will not bake with a dome on them. They will bake flat. Don't panic that you did anything wrong if the layers do not puff up in the middle.
Once baked, set on wire racks to cool for 10-15 minutes, then turn the cakes out onto the racks and let them cool out of the pans completely before adding filling and frosting.