Preheat oven to 375°.

Grease and dust 13x18-inch jelly-roll pan or 13x9 pan

In a large bowl combine dry ingredients: flour, sugar, baking soda, xanthan gum, ground cinnamon and salt

In a small saucepan bring water, butter, and cocoa to a boil (for about 30 secs), stirring frequently.

Remove from heat and pour into flour mixture.

Mix until well-blended.

Add buttermilk, vanilla, and eggs; mix batter well.

Pour batter into prepared pan.

For jelly roll pan bake at 375° for 17-20 minutes or until a toothpick comes out clean.

For 13x9 pan bake at 375° for 24-27 minutes or until a toothpick comes out clean.

To prepare the icing, combine butter, milk, and cocoa in a medium saucepan.

Bring to a boil, stirring constantly.

Remove from heat and gradually stir in powdered sugar (about 1/3 cup at a time), walnuts or pecans, and 2 teaspoons vanilla.

Spread over hot cake.

Frosting will cool and set in about 30 minutes. It will be completely firm in 1-2 hours.

Eat warm or wait to fully set; either way its wickedly good!