Lightly grease a 9-inch round cake pan & line the bottom with parchment paper.  Preheat oven to 375°F.

To prepare the cake batter, place the chocolate chips and butter in a medium to large sized microwave-safe mixing bowl. Microwave for 30 seconds at a time, stirring in between, until everything is melted and smooth.  Add the sugar, cocoa powder, eggs, and vanilla extract.  Use a handheld mixer to beat together until just combined.  Do not over mix.  Scrape the sides and bottom of the bowl to ensure everything is mixed in.

Pour the batter into the prepared cake pan.  Bake for 25 minutes in the preheated oven.  Let the cake cool in the pan for 5 minutes.  Run a knife around the edges to loosen, and flip the cake onto a serving platter or cake stand.  Let cool completely.

Make the ganache by placing the chocolate chips in a mixing bowl.  Pour the heavy cream into a microwave-safe bowl and heat in the microwave until simmering, about 45 seconds.  Pour the hot cream over the chocolate chips. Let stand for 2 minutes, then stir until smooth.

Spread the ganache evenly over the top of the cake.  Let cool before slicing and serving.  Best when served at room temperature.