Preheat your oven to 350°F (175°C) and generously grease and flour a Bundt pan.
In a large bowl, sift together flour, cocoa powder, baking powder, baking soda, and salt.
In another large mixing bowl, whisk together the sugar, buttermilk, vegetable oil, eggs, and vanilla extract until smooth.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Carefully stir in the hot water (or coffee) until the batter is smooth and slightly thin.
Pour the batter evenly into the prepared Bundt pan.
Bake for 50-55 minutes, or until a toothpick inserted into the center comes out clean.
Let the cake cool in the pan for 10-15 minutes, then invert onto a wire rack to cool completely.
Once fully cooled, dust with powdered sugar or drizzle with chocolate glaze.