Preheat the oven to 350 degrees Fahrenheit. Prepare 3, 6 inch cake pans with cooking spray and line the bottoms with parchment paper.
In a large bowl, melt the chocolate and butter together in the microwave in 30 second intervals, stirring after each time, until fully melted.
Stir in the sugars until well combined.
Whisk in the eggs, one at a time, until combined.
Add the flour, cocoa powder, espresso powder, baking powder and salt and stir until just combined, without overmixing.
Evenly divide the batter between the 3 cake pans and smooth the tops.
Bake for 30-35 minutes until a cake tester inserted into the middle comes out with moist crumbs and not shiny batter. Start checking the cakes around the 25 minute mark.
Remove the cakes from the oven and let cool for at least 20 minutes on a wire rack in the pan. Then turn the cakes out onto the rack to cool completely. If not using right away, the cakes can be wrapped in plastic wrap and stored in the refrigerator overnight.