Step 1

Preheat oven to 325 degrees F. Lightly coat a 9x13-inch baking pan with cooking spray; set aside.

Step 2

In a large saucepan, melt butter over medium heat. Whisk in the cocoa and espresso powder, followed by the water and sugar, whisking each addition until smooth. Remove pan from heat and set aside to cool for about 5 minutes.

Step 3

In a medium bowl, combine flour, cinnamon, baking soda, salt, pepper, and chocolate chips; mix briefly and set aside.

Step 4

Return to the butter-chocolate mixture. Add eggs and vanilla, then whisk until they are fully incorporated. Gently stir in the flour mixture using a wooden spoon or rubber spatula, then pour batter into the prepared pan.

Step 5

Bake for 30-35 minutes, until a toothpick inserted into the center comes out clean. Remove from the oven and let cool completely before frosting.

Step 6

To make the frosting, beat butter until smooth using a stand or electric mixer. Add salt and vanilla, then beat again to incorporate.

Step 7

Add powdered sugar and 2 tablespoons milk, and beat until smooth and fluffy, starting on low speed to blend, then increasing the speed to high. Scrape the sides of the bowl as needed to ensure everything is well-mixed, and adjust the consistency as needed by adding more milk or powdered sugar. Finally, beat in the cinnamon.

Step 8

Frost and garnish cake as desired.