Preheat the oven to 350°F. Generously butter and flour a 10 or 12 cup bundt pan, making sure every crevice is well coated. Set aside.
In a medium saucepan over low heat, combine the butter, cocoa powder, salt, and water. Heat just until the butter is melted, stirring to combine. Remove from the heat and set aside to cool slightly.
In a large mixing bowl, whisk together the flour, sugar, baking soda, and baking powder until combined.
Pour the warm chocolate mixture into the dry ingredients and stir until fully combined.
Add the buttermilk, eggs, and vanilla extract. Mix until the batter is smooth and fully combined.
Pour the batter evenly into the prepared bundt pan. Bake for 40 minutes, or until a toothpick inserted into the center comes out clean.
Remove the cake from the oven and allow it to cool in the pan for 5 minutes. Carefully invert the cake onto a wire rack and let it release naturally. Cool completely before adding the glaze.