Preheat the oven to 350°F (175°C). Grease and flour a 10-inch bundt pan, tapping out excess flour.
In a medium bowl, sift together the flour, baking powder, baking soda, salt, and cocoa powder. Set aside.
In a large bowl, using an electric mixer, cream the softened butter and granulated sugar together until light and fluffy, about 3-4 minutes.
Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract.
Alternately add the dry ingredients and buttermilk to the butter mixture, beginning and ending with the dry ingredients. Mix until just combined.
Slowly add the hot water to the batter, mixing on low speed until smooth. The batter will be thin.
Pour the batter evenly into the prepared bundt pan.
Bake for 50 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for 15 minutes, then invert onto a wire rack to cool completely before serving.