Preheat oven to 350°F (175°C). Grease and flour two 8-inch round cake pans; line bottoms with parchment rounds.
In a large bowl, whisk flour, sugar, black cocoa, baking powder, baking soda, and salt.
Add eggs, buttermilk, and oil; beat on medium speed for 2 minutes, then stir in hot coffee by hand until smooth.
Divide evenly between pans and bake for 30 to 35 minutes until a tester comes out clean; cool in pans for 10 minutes, then invert onto racks to cool completely.
Beat butter and powdered sugar with heavy cream and orange gel color for 5 minutes until fluffy.
Spread orange frosting between cake layers and over exterior; chill cake for 30 minutes.
Pour cooled chocolate ganache around top edges to create drips; decorate with festive sprinkles before serving.