Preheat oven to 350°F. Grease two 9-inch round cake pans and line bottoms with parchment paper.
In a large bowl, whisk together flour, sugar, cocoa powder, baking soda, baking powder, 1 teaspoon cinnamon, and salt until well combined and no lumps remain.
Add eggs, milk, oil, and vanilla to dry ingredients. Mix on medium speed for 2 minutes until smooth and well combined.
Carefully stir in hot coffee or hot water. The batter will be thin - this is correct.
Divide batter evenly between prepared pans. Bake for 30-35 minutes until a toothpick inserted in center comes out clean or with few moist crumbs.
Cool in pans for 10 minutes, then transfer to wire racks. Cool completely before frosting.
For frosting, beat softened butter on medium-high speed for 3-4 minutes until light and fluffy.
Gradually add powdered sugar, 2 teaspoons cinnamon, cayenne (if using), and 2 tablespoons cream. Beat until smooth, adding more cream if needed for spreadable consistency.
Place one cake layer on serving plate. Spread with frosting. Top with second layer and frost top and sides of cake.