Step 1: Prepare the Oven and Pan.

Preheat the oven to 350°F (175°C). This ensures that the oven is at the correct temperature when you’re ready to bake.

Spray a 9-inch round cake pan with nonstick baking spray. Make sure to coat the bottom and sides evenly.

Line the bottom of the pan with a circle of parchment paper. This provides extra insurance against sticking.

Spray the parchment paper with nonstick baking spray as well. Set the pan aside.

Step 2: Combine the Dry Ingredients.

Sift the flour, sugar, cocoa powder, baking soda, baking powder, and salt into a large bowl. This removes any lumps. It ensures that the ingredients are evenly distributed.

Whisk the sifted ingredients together to combine. This creates a homogenous dry mixture.

Step 3: Combine the Wet Ingredients.

In a separate large bowl, whisk together the buttermilk, oil, egg, and vanilla extract. Whisk until well combined.

Step 4: Combine Wet and Dry Ingredients.

Gradually add the flour mixture to the buttermilk mixture. Whisk until well combined. The batter will be thick.

Add the cooled coffee. Whisk just until evenly incorporated. Don’t overmix. The batter will become thinner.

Step 5: Bake the Cake.

Transfer the batter to the prepared cake pan. Spread it evenly with a spatula.

Bake for 28 to 32 minutes. Or until a wooden toothpick inserted in the center comes out clean.

Baking time may vary depending on your oven. Start checking for doneness at 28 minutes.

Step 6: Cool the Cake.

Let the cake cool in the pan for 15 minutes. This allows the cake to set slightly.

Invert the cake onto a cooling rack. Remove the parchment paper.

Let the cake cool completely, about 1 hour. Complete cooling is essential before adding the ganache.

Step 7: Make the Chocolate Ganache.

In a 4-cup heat-proof liquid measuring cup with a spout, combine the chocolate chips and 1 tablespoon of butter.

In a small saucepan, combine the heavy cream and light corn syrup.

Bring the cream mixture to a low simmer over medium-low heat. Do not boil.

Pour the hot cream mixture over the chocolate and butter. Let it stand for 2 minutes.

Stir until very smooth. The ganache should be glossy and pourable.

Set aside until cooled slightly, but still pourable (about 105°F/40°C), 2 to 5 minutes.

Step 8: Prepare for Ganache Pour.

While the chocolate ganache is cooling, set the cake, still on the wire rack, in a rimmed baking sheet. This will catch any excess ganache.

Step 9: Pour the Ganache.

Once the ganache has cooled slightly, pour it over the cake. Make sure to completely cover the top and sides.

Let any excess ganache run off into the rimmed baking sheet.

Smooth the top of the cake using a large offset spatula. This creates a professional finish.

Step 10: Chill the Cake.

Immediately transfer the cake to the refrigerator to harden the ganache, for 30 minutes. This sets the ganache.

Step 11: Transfer and Serve.

Using 2 large spatulas, carefully transfer the cake to a serving platter.

Serve slightly chilled or at room temperature.

Step 12: (Optional) Make and Add the Peanut Butter Ganache Swirl.

While the chocolate ganache is cooling, combine the peanut butter chips and butter in a small microwavable bowl.

Microwave on high until the mixture is melted and smooth, about 30 seconds. Stop to stir after 15 seconds.

Transfer the peanut butter mixture to a small Ziploc bag. Cut a 1/4-inch hole in one corner.

Immediately after covering the cake with warm chocolate ganache, pipe 6 equally spaced lines of the peanut butter mixture across the top of the cake.

Using a paring knife or skewer, drag the tip through the peanut butter and ganache in 7 evenly spaced lines perpendicular to the piped peanut butter. Alternate the direction of each line. This creates a swirl pattern.

Proceed with chilling the cake as directed.