Step 1

Preheat oven to 350 degrees. Spray a 9 by 9 or 8 by 8-inch baking dish with non-stick cooking spray then dust with cocoa. Shake out excess cocoa.

Step 2

In a large mixing bowl whisk together flour, sugar, 6 Tbsp cocoa, the baking soda, and salt.

Step 3

Add buttermilk, oil, vanilla and eggs.

Step 4

Whisk mixture until very well blended (about 1 minute).

Step 5

Pour into prepared baking dish.

Step 6

Bake in preheated oven until toothpick inserted into the center of cake comes out clean, about 27 to 35 minutes.

Step 7

Let cool completely on a wire rack.

Step 8

Meanwhile make ganache. Place finely chopped chocolate in a medium heat proof mixing bowl.

Step 9

Heat heavy cream in a small saucepan over stovetop on medium heat until just simmering.

Step 10

Pour hot cream over chocolate chocolate then stir with a rubber spatula until melted and smooth. Let it cool until it's a thicker consistency, about 30 minutes* then spread over cake and slice.