Preheat oven to 350°F. Prepare two 8x8-inch baking pans with butter and flour.

In a medium bowl, sift together flour, cocoa, baking powder, baking soda, and salt.

In a small bowl, whisk together buttermilk and pumpkin puree until combined.

In a mixer, beat butter, sugars, and vanilla until light and fluffy. Add eggs one at a time.

Alternately add flour mixture and pumpkin mixture to the butter mixture, beginning and ending with flour.

Divide batter evenly into prepared pans and bake for 18-26 minutes or until a toothpick comes out clean.

In a stand mixer, whip heavy cream on medium-high until soft peaks form. Gradually add confectioners' sugar and fold in pumpkin spice.

Heat heavy cream and pour over chocolate chips. Stir until smooth to make ganache.