Preheat oven to 350 degrees F. Generously grease a 15x10x1-inch baking pan; set aside.
Dissolve espresso powder in the boiling water. In a medium saucepan combine brewed espresso, butter, and unsweetened cocoa. Bring to boiling over medium-high heat, stirring constantly. Remove from heat; let cool for 10 minutes.
In a large bowl whisk together the sugar and flour. Add the warm cocoa mixture; stir to blend well. Add eggs, buttermilk, baking soda, vanilla, cinnamon, and salt; mix well. Spread batter evenly into prepared pan.
Bake for 20 to 25 minutes or until a wooden toothpick inserted near the center comes out clean. Immediately frost hot cake with warm Mocha Frosting. Sprinkle with pecans. Cool to room temperature before cutting.