Preheat oven to 175°C (350°F). Grease and flour a 9-inch round cake pan.
In a large bowl, whisk together flour, cocoa powder, baking powder, baking soda, cinnamon, cayenne, and salt.
In another bowl, beat the eggs with granulated sugar and brown sugar until light and fluffy. Add oil, buttermilk, and vanilla extract. Mix well.
Gradually add the dry mixture into the wet mixture, stirring gently until combined.
Slowly pour in the hot coffee and mix until smooth. Batter will be thin.
Pour the batter into the prepared pan and bake for 30–35 minutes or until a toothpick comes out clean.
Let the cake cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.
(Optional) Top with chocolate ganache or whipped cream with cinnamon.