Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a large bowl, sift together the flour, cocoa powder, baking powder, baking soda, and salt. Set aside.
In a separate large mixing bowl, whisk the eggs, granulated sugar, and brown sugar until smooth and slightly fluffy.
Add the milk, vegetable oil, and vanilla extract to the egg mixture and whisk until combined.
Stir in the hot brewed espresso and orange zest.
Gradually add the dry ingredients to the wet ingredients, mixing gently until just combined.
Slowly pour in the boiling water while stirring carefully to create a smooth batter.
Fold in the sour cream until fully incorporated.
Divide the batter evenly between the prepared cake pans.
Bake for 30 to 35 minutes, or until a toothpick inserted into the center comes out clean.
Remove the cakes from the oven and let them cool in the pans for 10 minutes.
Turn the cakes out onto wire racks and cool completely before frosting or serving.