Preheat oven to 350°. Lightly spray 8 x 8 inch square pan with cooking spray.
In a small bowl combine flour, xanthan gum (if using), salt, baking powder, and cocoa. Mix and set aside.
In using a standing or hand mixer, combine butter and eggs together. Add vanilla, both types of sugar and the food coloring, and mix until fully blended. Slowly mix in flour mixture and water. Once all flour is combined, spread evenly into pan.
Bake on center rack for 30-35 minutes or until toothpick comes out with just a few crumbs.