Cooking spray, as needed
1/4 cup unsalted butter
2/3 cup packed brown sugar
1 1/3 cups smoothly mashed very ripe banana, about 3 bananas
1 teaspoon vanilla
1 1/3 cups gluten-free flour with xanthan gum or 1 1/3 cups gluten-free flour mixed with 1 1/2 teaspoons xanthan gum (see note)
2 teaspoons dried egg whites
1 teaspoon cinnamon
1 teaspoon baking powder
1 teaspoon baking soda
3/4 teaspoon salt
1/4 teaspoon ground allspice
Heat oven to 350 F. Spray a 9-by-9-inch baking pan with cooking spray. Line bottom of pan with parchment paper; spray parchment with cooking spray.
In a medium bowl with an electric mixer, beat the butter with the brown sugar until fluffy. Add the eggs, 1 at a time, beating well after each addition. Add the bananas and vanilla; beat well.
In another medium bowl, whisk the flour with the dried egg whites, cinnamon, baking powder, baking soda, salt and allspice. Add dry ingredients in batches to banana mixture, beating well after each addition. Batter will be very thick; beat only enough to mix well.
Scrape batter into prepared pan and smooth with a spatula. Bake in preheated oven until a wooden pick inserted in center comes out clean, for 30 to 35 minutes. Remove from oven and cool on a rack. When cool, cut into 3-inch squares. Makes 9 bars.
NOTE: Xanthan gum can be found at health-food stores and grocers' natural-foods sections; it adds volume and moisture to gluten-free baked goods.
— Recipe adapted by the Chicago Tribune from "Cooking for Your Gluten-Free Teen."