Prep: Preheat the oven to 175°C / 350°F. Butter and flour two 15 cm (6” pans) or one 22 cm (8” pans), then line the bottom with parchment paper.
Wet mix: Mix eggs and sugar until pale and fluffy. Then add vanilla extract.
Dry mix: In another bowl, whisk together flour, sugar, cocoa, baking soda, salt, baking powder, and walnuts.
Combine: Add the dry ingredients to the wet and mix until just combined. Stir in the hot coffee until the batter will thin out.
Bake: Divide into pans and bake 22–25 minutes, until a toothpick comes out clean. Let cool completely.
Frosting: In a saucepan, melt butter, chocolate, and cream over medium heat, stirring until smooth. Sift in powdered sugar, cocoa, and salt. Stir well, then add vanilla. Pour into a bowl, cover the surface with plastic wrap, and cool (30 min room temp, then 1–2 hrs in the fridge) until spreadable.
Assemble: You can choose to whip the frosting with an electric mixer to make it fluffier and more spreadable. Trim the cake tops if needed. Spread frosting between the layers and all around the cake. Sprinkle with flaky salt if you like. Serve and devour.
