Preheat oven to 350 degrees.
Lightly grease two 8 inch cake pans withnonstick spray, then add cocoa powder and tap around until the pan is wellcoated.
Place the 1 ½ cups cocoa powder in a medium,heat-proof bowl. Whisk in the boiling water until fully combined. Stir in milk and set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream the butter and sugar on medium-low speed until lightand fluffy, 4-5 minutes. Add the eggs one at a time mixing until each is fully incorporated before adding the next. Scrape the bowl well. Add the vanilla and mix to combine.
In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Add one third of the mixture to the mixer and mix on low speed to combine. Add half of the cocoa/milk mixture and mix to incorporate. Repeat, alternating between the dry and wet ingredients, until both are fully mixed in and the batter is smooth.
Divide the batter between prepared pans. Bakethe cakes until a toothpick inserted into the center comes out clean, 30-40minutes. Cool the cakes in the pan for 10-15 minutes, then turn out onto a wirerack to cool completely.