Step 1

Preheat oven to 350° F. Line a 9-by-9-inch square baking pan with aluminum foil and spray with cooking spray, or grease and flour the pan; set aside.

Step 2

In a large mixing bowl combine egg, sugar, yogurt, oil, vanilla, and whisk until smooth and combined.

Step 3

Add coffee, cocoa powder (I used Hershey’s), and whisk vigorously until batter is smooth and free from lumps.

Step 4

Add the flour, baking soda, baking powder, salt, and whisk vigorously until batter has just combined, about 1 minute.

Step 5

Pour batter, which is a loose and fairly runny batter, into prepared pan and bake for about 25 minutes, or until top has set and a toothpick or cake tester inserted in the center comes out clean.

Step 6

Allow cake to cool in pan completely, at least 30 minutes, before adding ganache or frosting the cake, or before slicing and serving.

Step 7

Place chocolate in a medium microwave-safe bowl and heat on high power for 1 minute to soften chocolate; set aside.

Step 8

In a small microwave-safe bowl or measuring cup, heat the cream (I used half-and-half) on high power just until it begins to bubble and show signs of boiling, about 60 to 75 seconds.

Step 9

Pour hot cream over chocolate and let it stand about 1 minute. Whisk vigorously until chocolate has melted and mixture is smooth and velvety.

Step 10

Add vanilla or optional flavorings and stir to combine. Set bowl aside for about 10 minutes, allowing ganache to cool and thicken a bit.

Step 11

Whisk mixture briefly before pouring all of it over the cake. Lightly smooth and spread the ganache with a spatula or offset knife.

Step 12

Allow ganache to set up for at room temperature for at least 30 minutes before slicing and serving the cake; or speed this process up by placing pan in the refrigerator or freezer briefly.