Preheat your oven to 350°F (175°C). Grease and flour your Bundt pan to ensure the cake releases easily.

In a large mixing bowl, whisk together the flour, sugar, cocoa powder, baking soda, and salt.

In a saucepan, melt the butter over medium heat, then add the water. Bring the mixture to a boil, and once boiling, pour it over the dry ingredients. Stir until combined.

In a separate bowl, mix the buttermilk, eggs, and vanilla extract. Slowly add this mixture to the cake batter, stirring until well combined.

Pour the batter into the prepared Bundt pan and smooth the top with a spatula.

Bake in the preheated oven for 30-35 minutes or until a toothpick inserted comes out clean. Allow the cake to cool in the pan for about 10 minutes before turning it out onto a wire rack.

While the cake cools, prepare the frosting. In a saucepan, melt the butter and then add milk and cocoa powder. Stir to combine and bring to a simmer. Remove from heat and mix in the powdered sugar and vanilla extract until smooth.

Pour the warm frosting over the cooled Bundt cake, allowing it to drizzle down the sides beautifully.