Preheat oven to 350 degrees
Whisk together the melted butter and sugar until full combined
Add cocoa powder, salt, baking powder, vanilla extract and expresso powder and whisk to combine
Add in eggs, one at a time, and beat batter until smooth and fully combined
Add water and whisk
Add flour and stir until full incorporated
Grease a 6" springform pan
Transfer the batter into the greased springform
Bake for 25 minutes at 350 degrees or until a toothpick comes out clean from the center
Transfer the springform onto a cooling rack to cool before adding the next layer