2 cups all-purpose gluten-free flour
1 teaspoon xanthan gum (omit if your blend already contains it)
3/4 teaspoon kosher salt
1 teaspoon baking powder
1/2 teaspoon baking soda
2/3 cup granulated sugar
8 tablespoons unsalted butter, melted and cooled
2 eggs at room temperature, beaten
1 teaspoon pure vanilla extract
2/3 cup sour cream, at room temperature
1 cup ripe bananas, peeled and mashed lightly (from about 2 medium-size bananas)
Preheat your oven to 350°F. Grease a standard 9 x 5 inch loaf pan, and set it aside.
In a large bowl, place the flour, xanthan gum, salt, baking powder, baking soda and sugar, and whisk to combine well. Add the butter, eggs and vanilla, then the sour cream, mixing until just combined after each addition. Add the mashed bananas and fold them into the batter, taking care not to further mash the bananas.
Scrape the batter into the prepared loaf pan, and smooth the top with a wet spatula. Place the pan in center of the preheated oven and bake until golden brown on top, and a toothpick inserted in the center comes out with no more than a few moist crumbs attached (about 45 minutes). If the loaf is browning too fast for the center to bake fully, tent with foil while it finishes baking. Allow to cool in the pan for 10 minutes before transferring to a wire rack to cool completely before slicing and serving.