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

In a large mixing bowl, whisk together the flour, sugar, cocoa powder, baking powder, 1 teaspoon of the cinnamon, cayenne pepper, and salt.

Add the eggs, milk, vegetable oil, and vanilla extract to the dry ingredients. Beat with a mixer on medium speed for about 2 minutes.

Stir in the boiling water by hand until well combined; the batter will be thin and watery, which is normal.

Pour the batter into the prepared pan(s) and bake for 30 to 35 minutes, or until a toothpick inserted into the center comes out clean.

Remove the cake from the oven and let it cool completely on a wire rack before frosting.

To make the ganache, place the chocolate chips and remaining 1/2 teaspoon of cinnamon in a small heatproof bowl.

Heat the heavy cream in a small saucepan until it just begins to simmer, then pour it over the chocolate chips.

Let the mixture sit for 5 minutes, then whisk gently until smooth and glossy.

Pour the warm ganache over the cooled cake, spreading it evenly with a spatula, and allow it to set slightly before serving.