Grease a 13-by-9-inch baking pan; set aside. In a medium mixing bowl combine the flour, sugar, baking soda, cinnamon, and salt; set aside.
In a medium saucepan combine 1 cup butter, water and 1/3 cup cocoa powder. Bring mixture just to boiling, stirring constantly. Remove from heat. Add the chocolate mixture to the flour mixture; beat with an electric mixer on medium speed until combined. Add eggs, 1/2 cup buttermilk and 1-1/2 teaspoons vanilla. Beat for 1 minute (batter will be thin). Pour batter into the prepared pan, spreading evenly.
Bake brownies at 350 degrees for 35 minutes or until a wooden toothpick inserted in the center comes out clean.
To make frosting: In a medium saucepan combine 1/4 cup butter, 3 tablespoons unsweetened cocoa powder and 3 tablespoons buttermilk. Bring mixture to boiling. Remove from heat. Add powdered sugar and 1/2 teaspoon vanilla.
Beat until smooth. If desired, stir in pecans. Pour warm frosting over the warm brownies, spreading evenly. Cool on a wire rack. Cut into bars and serve.