Step 1

Preheat oven to 350F. Generously grease one 6-inch Bundt cake pan with cooking spray or rub the pan with butter.

Step 2

Add about an inch of water to a pan and bring to a simmer. Turn off the heat and place a heatproof bowl over top. Add the chopped chocolate and melt until smooth. Remove from the heat and cool for 10 minutes.Alternatively, add chocolate to a microwave-safe bowl then microwave for 30 seconds. Stir then continue microwaving in 15 second increments until melted and smooth.

Step 3

In a medium bowl, sift together the flour and cocoa then stir in the baking soda, espresso powder, and salt.

Step 4

In a large mixing bowl on medium-high speed (with paddle attachment if using stand mixer), beat together the butter, sugar, and brown sugar until light and creamy, about 1 minute.

Step 5

Scrape down the bowl then beat in the egg, vanilla, and melted chocolate.

Step 6

On the lowest speed possible, add the flour mixture alternately with the buttermilk and coffee, adding the flour in 3 additions and the liquid in 2 additions (begin and end with dry ingredients).When the flour is about 90% incorporated, stop the mixer and switch to a rubber spatula. Finish adding the flour by hand as you don't want to overmix the batter.

Step 7

Transfer the batter to the pan. Bake 30-35 minutes or until a toothpick inserted in the middle comes out clean.

Step 8

Cool for about 15 minutes, run a knife along the edge of the pan to loosen, and invert onto a cooling rack. Cool right-side-up.

Step 9

Once fully cooled, decorate with glaze or ganache. Store in an air-tight container at room temperature for up to 4 days (glaze only) or in the refrigerator for up to 1 week (glaze or ganache). For best results, let the refrigerated cake sit at room temperature 15-30 minutes before serving.