Preheat oven to 375 degrees. Grease an 8-inch round cake pan.

In a microwave safe bowl, heat the chocolate chips and butter until the chips are soft. Stir until the mixture is completely melted and smooth. Return to the microwave in 15 second increments if needed.

Transfer the melted chocolate mixture to a large mixing bowl. Stir in the sugar, salt, espresso powder and vanilla. Beat in the eggs.

Add the cocoa powder and mix until just combined.

Spoon the batter into the prepared pan. Bake for 25 minutes, or until the top forms a thin crust. Cool on a wire rack for 5-10 minutes.

Loosen the edges of the pan with a knife, then invert the cake onto a serving plate. Allow cake to cool completely.

Meanwhile, make the chocolate ganache. While the ganache is still pourable, spoon it onto the cake, then spread it to the edges and allow it to drip over the sides. Let stand for several hours, or until ganache is set.