For Cake

1. Preheat oven to 350°F. 
2. In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter and sugar on medium-high speed until light and fluffy, about 4 minutes. Scrape down the sides of the bowl. 
3. Add the eggs one at a time, mixing until well combined. Scrape down the sides of the bowl after each addition.
4. Add the vanilla and mix to combine well.
5. In a separate bowl, whisk together the flour, cocoa powder, baking soda, baking powder and salt.
6. Add the dry ingredients to the butter and egg mixture in three additions, alternating with the chocolate milk. Begin and end with the flour mixture. Do not overmix.
7. Remove the bowl from the stand mixer and use a large spatula to stir in the boiling hot water, again being careful not to overmix. 
8. Spray a 12 to 15 cup Bundt pan with non-stick baking spray. Carefully transfer the batter to the prepared pan and smooth the top with a spatula.
9. Bake for 45 to 50 minutes or until a toothpick inserted into the middle of the cake comes out clean or with a few crumbs remaining. If the cake is getting too dark towards the end of the baking cycle, cover it with aluminum foil to prevent over-browning.
10. Remove the cake from the oven and set the pan on a wire rack. Set a timer for exactly 10 minutes. After 10 minutes, lay a cake platter or wire cooling rack over the top of the cake pan and carefully invert the pan 180° in one swift motion. The cake should release easily.
11. Cool completely on a wire rack before drizzling with glaze.

For Glaze

1. Sift the powdered sugar into a large bowl.
2. Sift in the cocoa powder.
3. Add the chocolate milk and stir until smooth and shiny. If the glaze is too thick, add more chocolate milk. If too thin, add more powdered sugar. The glaze should be thick, but pourable.