Chocolate Pumpkin Cake

INGREDIENTS
1 1/2 cup(s) flour
2/3 cup(s) cocoa
2 teaspoon(s) baking powder
1 teaspoon(s) baking soda
1/2 teaspoon(s) salt
1/2 cup(s) buttermilk
1 cup(s) canned pumpkin
2 teaspoon(s) vanilla extract
3/4 cup(s) butter, softened
1 cup(s) dark brown sugar
1 cup(s) granulated sugar
3 large (plus one yolk) eggs

DIRECTIONS
1. Heat oven to 375 degrees. Line the bottoms of two 8-inch cake pans with parchment paper and lightly butter.
2. Sift the flour, cocoa, baking powder, baking soda, and salt together. Stir the buttermilk, pumpkin, and vanilla extract together in a small bowl. Beat the butter and sugars together using an electric mixer on medium speed until light and fluffy. Beat in the eggs and yolk, one at a time. Reduce mixer speed to low and alternately beat in the flour and buttermilk mixtures in thirds.
3. Pour the batter into the prepared pans. Bake until a tester, inserted in the center, comes out clean--about 35 minutes. Cool layers completely before icing.