Pre-heat the oven to 350°F.
Spray 3 round cake pans with cooking spray; dust the pans lightly with flour; set aside.
In a large mixing bowl, or mixer, combine the flour, Hershey's cocoa, sugar, baking powder, baking soda and salt.
Add the milk, oil, eggs and the vanilla extract; mix until everything is thoroughly incorporated.
Once all combined, stir in the boiling water last; mix again; the batter will be very thin.
Pour the batter evenly in each of the sprayed/floured cake pans.
Place in oven and bake for 30 to 35 minutes, or until a toothpick inserted in the center of each layer comes out clean.
Once fully baked, remove from oven and allow the 3 cakes to cool for at least 10 to15 minutes before removing from pans.
Once removed, transfer to a wire rack to finish cooling completely.
While they finish cooling, prepare the buttercream frostings.