Preheat oven to 175°C / 350°F. Grease and line two 8-inch (20 cm) round cake pans.
In a large bowl, whisk together flour, cocoa powder, sugar, baking powder, baking soda, and salt.
Add eggs, milk, oil, and vanilla. Mix until smooth.
Slowly pour in the hot coffee (or water), mixing gently. The batter will be thin—this is key for moisture.
Divide evenly between pans and bake for 30–35 minutes, or until a toothpick comes out with a few moist crumbs.
Cool in pans for 10 minutes, then turn out onto a rack to cool completely.
In a saucepan over medium heat, melt butter with cream and sugar, stirring until smooth.
Add cocoa powder and whisk until glossy and thick.
Remove from heat; stir in vanilla and salt. Let cool slightly until spreadable but still pour-smooth.
Place one cake layer on a plate, spread frosting generously on top.
Add the second layer and pour the remaining frosting over the top, letting it drip naturally down the sides.
