To prepare cake, coat a sheet pan with cooking spray and dust with the 2 teaspoons flour.
Combine 2 cups flour, granulated sugar, baking soda, cinnamon, and salt in a large bowl. Stir well with a whisk.
Combine water, 1/2 cup butter, and 1/4 cup cocoa in a small saucepan. Bring to a boil, stirring frequently. Remove from heat, pour into flour mixture. Beat with a mixer at medium speed until well blended. Add buttermilk, 1 teaspoon vanilla extract, and eggs. Beat well.
*If you do not have buttermilk, you can substitute nonfat milk and mayonnaise. In a half cup measuring cup, fill halfway with milk and then spoon in mayonnaise until full.
Pour batter into prepared pan and bake at 375 degrees for 17 minutes or until a wooden toothpick inserted in center comes out clean. Place on a wire rack.
To prepare icing, combine 6 tablespoons butter, milk, and 1/4 cup cocoa in a medium saucepan. Bring to a boil, stirring constantly. Remove from heat. Gradually stir in powdered sugar, pecans, and 2 teaspoons vanilla extract. Spread over hot cake. Cool completely on wire rack.
You can also make this cake in a 13x9 baking pan. Bake at 375 degrees for 22 minutes.