Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans and set aside.
In a large mixing bowl, sift together the all-purpose flour, unsweetened cocoa powder, granulated sugar, baking powder, baking soda, and salt.
In a separate medium bowl, whisk the eggs, whole milk, vegetable oil, and vanilla extract until well combined.
Add the wet ingredients to the dry ingredients and mix until just combined.
Slowly pour in the hot espresso while stirring gently to incorporate the coffee flavor evenly.
Add the freshly grated orange zest and mix gently.
Carefully add the boiling water to the batter and stir until smooth. The batter will be thin; this is normal.
Divide the batter evenly between the prepared cake pans.
Bake in the preheated oven for 30 to 35 minutes, or until a toothpick inserted into the center comes out clean.
Remove the cakes from the oven and allow them to cool in the pans for 10 minutes.
Turn the cakes out onto wire racks and cool completely before frosting or serving.