Preheat oven to 350°F. Grease and flour two 9-inch round cake pans or line with parchment paper.
In a large bowl, whisk together flour, sugar, cocoa powder, baking powder, baking soda, cinnamon, cayenne pepper, and salt until well combined and no lumps remain.
In a stand mixer or separate bowl, combine buttermilk, oil, eggs, and vanilla extract. Mix on medium speed for 30 seconds until well blended.
With mixer on low, gradually add dry ingredients to wet ingredients. Once incorporated, carefully pour in hot coffee while mixing. Batter will be thin.
Divide batter evenly between prepared pans. Bake for 30-35 minutes until toothpick inserted in center comes out with few moist crumbs.
Cool in pans for 10 minutes, then turn out onto wire racks to cool completely before frosting.
For frosting, beat butter in stand mixer on medium-high for 2 minutes until pale and fluffy.
Add cinnamon and vanilla, mix until combined. Gradually add powdered sugar one cup at a time on low speed.
Increase mixer to high speed and beat for 2 minutes. Add heavy cream one tablespoon at a time until desired consistency is reached.
Frost cooled cake layers. Store in airtight container at room temperature for up to 2 days, then refrigerate.
