Preheat to 360F, butter an 8 inch cake pan and line with parchment paper.
Chop chocolate and butter then place in a bowl over a pot of simmering water and melt stirring occasionally. Sift in the cocoa powder, whisk in the sugar, salt, espresso powder and eggs mix very well. You may add a teaspoon of vanilla at this point but it is optional.
Pour into prepared pan and bake at 360f for 22-25 minutes. The top will have a crust and the edge will have risen and set.
Allow to cool in pan for a few minutes then run a knife along the edge and invert onto a cake plate. Allow to cool then dust with powdered sugar, cocoa or cover in ganache. Top with berries and enjoy!
An 8-inch cake pan works best, if you use a larger pan it will result in a thinner cake.
Use good quality chocolate and cocoa powder for best results.
Make sure to use a chocolate bar and not chocolate chips or candy melts because they contain additives that stop the chocolate from melting in a silky soft consistency.
If using semisweet chocolate reduce the amount of sugar to 2/3 cup.
There's no need to bring the butter to room temperature for this cake because it's melted with the chocolate.
I use unsalted butter because salt is added in separately. If you use salted butter make sure to reduce the added salt.
Make sure to grease the cake pan and line it with parchment paper so the cake doesn't stick.
Let the cake cool completely before adding any toppings.