preheat oven to 350°. Generously grease a 15 x 10" baking pan; set aside.
Dissolve espresso powder in the boiling water. In medium pan, mix brewed espresso, butter and unsweetened cocoa powder. 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. Makes 24 servings.
Mocha frosting: in a medium pan heat 1/3 cup butter, 1/2 cup buttermilk or milk, 1/3 cup unsweetened cocoa powder, and 1 teaspoon instant espresso coffee powder over medium low heat until butter melts, stirring constantly. Remove from heat. With electric mixer on medium speed beat in 4 1/2 cups powdered sugar and 1 teaspoon vanilla.