This recipe comes to use from Joy Mendez.
½ cup butter or margarine
1 cup granulated sugar
1 teaspoon vanilla extract
1 ½ cups mashed ripe bananas (about 3 medium)
1 ½ cups gluten-free flour mix
1 teaspoon baking powder
1 teaspoon baking soda
½ teaspoon salt
1 teaspoon xanthan gum
¼ cup baking cocoa
(optional: ½ cup chocolate chips added to the dark batter--I did this and the result is delicious)
In a mixing bowl, cream butter and sugar. Add egg and vanilla extract; beat until thoroughly combined. Blend in the bananas.
Combine the flour, baking powder, baking soda and salt; add to creamed mixture and mix well. Divide batter in half. Add cocoa to half; spread into a greased 13 x 9-inch baking pan. Spoon remaining batter on top and swirl with a knife. Bake at 350F for 25 minutes or until the bars test done.
Yields about 2 ½to 3 dozen bars.