Preheat oven to 350° F. Line a 8" square baking pan with parchment paper. Set aside.
In a large mixing bowl, whisk together flour, cocoa powder, baking powder, baking soda, brown sugar, granulated sugar, salt and pumpkin spice. Stir in chocolate chips.
In a large measuring cup, whisk together pumpkin puree, vanilla, egg, oil and buttermilk. Add to dry ingredients and whisk until batter is smooth. Pour batter into prepared pan. Tap gently against the counter to release any air bubbles.
Bake in pre-heated oven for 28 to 32 minutes or until the top of cake is dry and the toothpick inserted in the center of the cake comes out clean.
Cool completely in pan.
To make ganache:
Heat up cream in measuring cup, in microwave. Do not boil.
Place chocolate chips in a small mixing bowl. Pour cream over chips. Let stand for a few minutes. Stir until smooth.
Cool slightly, then pour over cake. Spread evenly. Cool completely. The ganache will set.
Notes
Serving is one piece per person.
Please note, that the nutrition value can vary depending on what product you use. The information below is an estimate.
If you don't have buttermilk on hand, simply mix 2 teaspoons of apple cider vinegar with ⅓ cup plus 1 teaspoon of half and half or whole milk. Let sit to sour, then use in the recipe.
I recommend semi-sweet chocolate chips for the ganache as the flavor will complement the cake better than milk chocolate chips.