Preheat oven to 175°C (350°F). Grease and line two 9-inch round cake pans.
In a large bowl, whisk flour, cocoa powder, sugar, baking powder, baking soda, and salt.
Add eggs, milk, oil, and vanilla extract. Mix until smooth.
Slowly pour in hot coffee and mix until combined (batter will be thin).
Divide batter evenly between prepared pans.
Bake for 30–35 minutes or until a toothpick inserted comes out clean.
Let cakes cool completely before frosting.
Frosting
Beat butter until creamy.
Add cocoa powder and powdered sugar gradually.
Pour in cream, vanilla, and salt. Beat until fluffy.
Frost cake layers, stack, and decorate as desired.