Heat oven to 350. Lightly spray a 9" x 13: baking pan w/ cooking spray. In lg bowl, combine flour, 2 cups sugar, cocoa, baking soda, salt and cinnamon.
In another bowl, whisk together buttermilk, oil, eggs and 1-1/2 tsp vanilla. Whisk buttermilk mix into flour mix. Whisk in coffee. Pour batter into pan. Bake 35 mins, or until a toothpick inserted in center comes out clean. Let cool.
In a saucepan bring sugar, milk and butter to boil over medium heat. Stir often. Pour into a lg bowl. Add chocolate chips and vanilla, stirring until chocolate is melted. Let sit a few minutes to thicken. Beat until smooth. Spread over cooled cake.