- 1 tablespoon unsalted butter
- 3 large eggs
- 2 cups granulated sugar
- 1 cup mayonnaise
- 1 teaspoon pure vanilla extract
- 1/3 cup unsweetened cocoa powder
- 1/2 teaspoon ground cinnamon, plus more for dusting
- 1/2 cup hot brewed coffee
- 1/2 cup cold water
- 2 cups all-purpose flour
- 1 1/2 teaspoons baking soda
- 2/3 cup mini chocolate chips
- Confectioners' sugar for dusting
- Preheat the oven to 350 degrees F. Butter a 9-x-13-inch baking pan, then line it with wax paper or parchment paper and butter the paper.
- Whisk together the eggs, sugar, mayonnaise and vanilla in a large bowl. Place the cocoa and cinnamon in a small heatproof bowl; whisk in the coffee and 1/2 cup of cold water until blended. Add the coffee mixture to the egg mixture in 3 parts, whisking to blend after each addition. Add the flour and baking soda and whisk until smooth. Stir in the chocolate chips.
- Pour the batter into the prepared pan. Bake the cake until a toothpick inserted in the center comes out clean, about 40 minutes. Let the cake cool for 10 minutes, then invert onto a rack and let cool for about 1 hour. Dust the cake with cinnamon, then confectioners' sugar, and cut into triangles.