In your serving mug, add the cocoa powder, sugar, ground cinnamon, and cayenne pepper. Stir the dry ingredients together.

Pour a small amount of the hot coffee into the mug. Whisk vigorously to form a smooth paste.

Slowly pour in the rest of your hot coffee, stirring as you go. Add the milk and the optional vanilla extract, and stir until everything is well combined.

Taste and adjust if needed. Top with whipped cream and chocolate shavings, if desired.