Gluten Free Banana Bread

This is the BEST Gluten Free Banana Bread that I have tried and I have tried a few. This is taken fromCD Kitchen.com

1 cup soy flour
1/2 cup potato starch
1/4 cup rice flour
1/2 tsp xanthan gum
1 tsp baking soda
1 1/4 tsp cream of tartar
1/2 tsp salt
1/3 cup butter - at room temp
2/3 cup sugar
2 eggs - well beaten
1 cup mashed banana (I use 3 large banana's)
1/2 cup chopped walnuts - optional

Set oven to 350 degrees. Butter loaf pan. In bowl, wisk together flour, startch, xanthan gum, baking soda, cream of tartar and salt. In an electric mixer cream the butter. Add sugar and beat until light and fluffy. Beat in eggs. With mixer on lowest speed beat in dry ingredients alternatly with the mashed banana and beat until smooth. Add nuts if using. Transfer the batter tothe prepared pan and smooth top. Bake the bread for 50-60 minutes or until a toothpick comes out clean. VERY IMPORTANT.. banana bread takes a long time to fully cook. Let cool on a rack for 20 minutes and turn out to cool completely. ENJOY. My kids LOVE this bread.. LOVE!