Preheat oven to 375 degrees F. Spray an 8-Inch round cake pan with nonstick cooking spray. Line the bottom with parchment and spray the sides and bottom again. Set aside.
In a microwave proof bowl combine the chocolate and butter in, and with 30 second increments, heat until the butter is melted and the chips are soft. Stir until the chocolate is melted and the mixture is smooth. Do this until completely combined.
With a whisk, whisk the sugar, and vanilla extract and stir to combine to the chocolate mixture.
While whisking, slowly start adding the beaten whole eggs until completely combined and smooth. Add the cocoa powder and whisk until just combined.
Pour the batter into the prepared pan, using an offset spatula, evenly distribute the batter to the sides of the pan. Bake the cake for 25 minutes or until the cake has a thin crust on the top
Let the cake cool in the pan for 10 minutes and then transfer the cake out of the pan and onto a wire cooling rack for 10 minutes. The cake can stay upside down!
While the cake is cooling, make the chocolate ganache. Place the cream in a medium microwave-safe bowl, and heat until the cream is hot and slightly bubbly, so it will melt the chocolate. I always start with 30 seconds and check it. It might take longer, it just depends on your microwave. Remove from the microwave, and add the chocolate , stir until everything melts and the mixture is smooth.
With the back of a spoon or a small offset spatula, spread the chocolate ganache evenly over the cooled cake. Let the glaze set up for a few hours before cutting and serving the cake, or place it in the fridge until it sets up.