6 tablespoons unsalted butter, at room temperature
1 cup granulated sugar, plus 1 tablespoon
2 eggs at room temperature, beaten
2 1/2 cups all-purpose gluten-free flour
1 teaspoon xanthan gum (omit if your blend already contains it)
1 teaspoon baking powder
1/2 teaspoon baking soda
3/4 teaspoon kosher salt
10 ounces fresh cranberries, halved
1/2 cup milk, at room temperature*
1/2 cup sour cream, at room temperature*
*The milk and sour cream together can be replaced by 1 cup (227 g) plain whole milk yogurt, or with 1 cup (8 fluid ounces) real buttermilk.
Preheat your oven to 350°F. Grease or line a standard 9 x 5-inch loaf pan and set it aside.
In the bowl of a stand mixer fitted with the paddle attachment, or a large bowl with a handheld mixer, place the butter. Beat on medium-high speed until light and fluffy. Add the 1 cup of granulated sugar and the eggs, beating well after each addition.
In a separate, medium-size bowl, place the flour blend, xanthan gum, baking powder, baking soda and salt, and whisk to combine well. Place the cranberry halves in a separate, small bowl. Add about one tablespoon of the dry ingredients to the cranberries, and toss to coat. Set the cranberries aside. To the bowl with the butter and sugar mixture, add the dry ingredients, alternating with the milk and sour cream, beginning and ending with the dry ingredients. The mixture will be thick but smooth. Add the cranberries and reserved dry ingredients, and mix gently into the batter until evenly distributed throughout.
Scrape the batter into the prepared pan, and smooth the top. It will nearly fill the pan. Smooth the top with a wet spatula, and sprinkle with the remaining tablespoon of sugar. Place the pan in the center of the preheated oven and bake, rotating once, until golden brown on top and a toothpick inserted in the center comes out clean (about 1 hour). Remove from the oven and allow to cool in the pan for 20 minutes before transferring to a wire rack to cool completely. Slice and serve.