• Preheat the oven to 375F.
• Prepare an 8-inch non-stick round cake pan.
• IMPORTANT: cut a circle out of parchment paper to fit the bottom of the cake pan, and put inside the pan. Do not skip this step, or the cake will stick.
• Spray the inside of the cake pan with a non-stick cooking spray (including the parchment paper and the sides of the pan).
• Put the butter and 1 cup of chocolate chips in a microwave-safe bowl, and heat for 1 minute. Stir. Continue heating and stirring in 30-second increments until the butter and chocolate are melted and combined.
• Put the chocolate and butter mixture in a large mixing bowl. Add sugar and espresso powder (if using). Add the eggs and whisk until smooth.
• Add the cocoa powder and mix until well combined.
• Pour the batter into the cake pan.
• Put in the oven and bake for 20 minutes.
• Remove the cake from the oven and let cool for 10 minutes.
• Run the knife around the edges of the cake to separate it from the pan. Put a large plate upside down on top of the cake pan, then quickly invert the cake onto a plate.
• Peel off and discard the parchment paper. Don't worry if the cake has cracks or the edges crumble - the chocolate glaze will hide all the imperfections.

Make the chocolate ganache glaze

• Put the heavy cream and 1 cup of chocolate chips in a small pot. Heat it over medium heat, stirring every minute, until the cream is hot and the chocolate chips are melted. (Do not allow the cream to boil, reduce heat if necessary). Stir the cream and chocolate until it's well combined and smooth.

Glaze the cake

• Spoon the chocolate glaze over the top and sides of the cake. Let the glaze cool for 30 minutes at room temperature, then refrigerate the cake for at least 1 hour to set the glaze.