Preheat oven to 375°F (190°C). Line an 8-inch round cake pan with parchment paper, letting excess extend over sides of pan. Butter and flour parchment.
In the top of a double boiler, combine chocolates and butter. Cook over simmering water, whisking constantly, until chocolate is melted and mixture is smooth; remove from heat. Add granulated sugar and eggs, whisking until combined. Stir in cocoa and red pepper. Pour batter into prepared pan.
Bake until a thin crust forms on top of cake, about 25 minutes. Let cool in pan for 10 minutes. Using excess parchment as handles, remove from pan, and let cool completely on a wire rack. Refrigerate for at least 4 hours. Dust with alternating layers of cinnamon, cocoa, and confectioners’ sugar, if desired.
Recipe by Bake from Scratch at https://bakefromscratch.com/mexican-flourless-chocolate-cake/