Preheat your oven to 350°F (175°C) and grease and flour two 9-inch round cake pans or a 9x13 inch baking pan.

In a large mixing bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, salt, cinnamon, and cayenne pepper until fully combined and no lumps remain.

Add the milk, vegetable oil, eggs, and vanilla extract to the dry ingredients.

Mix on medium speed with an electric mixer or whisk vigorously by hand for about 2 minutes until the batter is smooth and glossy.

Carefully stir in the boiling water by hand; the batter will become very thin and watery, which is normal and ensures a moist cake.

Pour the batter evenly into the prepared cake pans.

Bake for 30 to 35 minutes, or until a wooden toothpick inserted into the center comes out clean or with just a few moist crumbs.

Remove the cakes from the oven and let them cool in the pans for 10 minutes before transferring them to a wire rack to cool completely.

Serve slices plain, dusted with powdered sugar, or frosted with a simple chocolate ganache.