Melt butter in a large saucepan over medium-high heat for 5-10 minutes until golden brown.

Remove from heat and add 1/4 cup black cocoa powder and vanilla extract. Stir to combine and let cool. Preheat oven to 350°F.

In a medium bowl, combine white sugar and the zest of 2 oranges. Massage together with your fingers until you have a fragrant, orange-colored sugar.

Add your orange sugar to the melted brown butter mixture and stir to combine. Then, add your eggs, one at a time, until mixed.

In a large bowl, sift together AP flour, 1/4 cup black cocoa powder, kosher salt, baking soda, and baking powder.

In another medium bowl or pyrex cup, whisk together buttermilk, coffee, and vegetable oil.

Alternate adding your dry ingredients and coffee milk mixture to the butter batter, starting and ending with your flour mixture. Fold the last batch of flour into the batter with a spatula until just combined.

Grease and line a 9 x 9 square baking pan with parchment paper. Pour in your cake batter and bake for 30 - 35 minutes until the top springs back.

To make frosting, chop your chocolate and add to a heat-proof bowl. Add the zest of 2 oranges and set aside.

In a medium stock pot, heat your heavy cream over medium-high heat until scalding and starting to bubble. Pour over your chocolate and orange zest and let sit for 1 minute to melt.

Whisk your ganache into a silky smooth, glossy mixture. If there are chunks of unmelted chocolate, place back in the stock pot and melt over medium heat until homogenous.

Let your ganache cool for 30 - 60 minutes in the fridge until barely firm and cool to the touch. Whip the ganache with a hand mixer for 30 seconds until fluffy and paler in color.

Spread your frosting over your cooled chocolate cake with an offset spatula. Slice into 9 equal squares and top each with a half slice of fresh orange.