For the quick bread
1 3/4 cups (245 g) all purpose gluten free flour (I used Better Batter)
1 teaspoon xanthan gum (omit if your blend already contains it)
1/4 cup + 2 tablespoons (54 g) cornstarch
1 1/2 teaspoons baking powder
1/2 teaspoon baking soda
1/2 teaspoon kosher salt
3/4 cup (150 g) granulated sugar
6 tablespoons (84 g) unsalted butter, at room temperature
1 cup (8 fluid ounces) buttermilk, at room temperature
2 eggs (100 g, weighed out of shell) at room temperature, beaten
1 teaspoon pure vanilla extract
For the cinnamon-sugar mixture
1/2 cup (100 g) granulated sugar
2 teaspoons ground cinnamon
For the (optional) glaze
1 cup (115 g) confectioners’ sugar
1 tablespoon milk (any kind), plus more by the 1/4 teaspoonful if necessary
Preheat your oven to 350°F. Grease and line with unbleached parchment paper a standard 9-inch x 5-inch loaf pan and set it aside.
Make the quick bread batter. In a large bowl, place the flour, xanthan gum, cornstarch, baking powder, baking soda, salt and sugar, and whisk to combine well. Create a well in the center of the dry ingredients and add the butter, buttermilk, eggs, and vanilla, mixing to combine after each addition. The batter will be thick and fluffy.
Make the cinnamon-sugar mixture and assemble. In a small bowl, place the granulated sugar and cinnamon, and mix to combine well. Scrape half of the quick bread batter into the prepared loaf pan, and spread into an even layer with a wet spatula. Place half of the cinnamon-sugar mixture on top and shake into an even layer. Place the remaining batter on top followed by the remaining cinnamon-sugar mixture, in the same manner. Using a wet butter knife at an angle perpendicular to the bottom of the loaf pan, carefully swirl the batter in all directions. The top of the batter should be craggy and uneven.
Bake the loaf. Place the loaf pan in the center of the preheated oven and bake for 30 minutes at 350°F. Lower the oven temperature to 325°F, rotate the loaf pan 180°, and continue to bake until a toothpick inserted in the center of the loaf comes out with no more than a few moist crumbs attached, and the top is light golden brown and firm to the touch (about another 15 minutes). Remove from the oven and allow to cool in the baking pan for 15 minutes before transferring to a wire rack to cool completely.
Make the glaze while the quick bread is cooling. In a small bowl, place the confectioners’ sugar and 1 tablespoon of milk. Mix well, until a thick paste forms. Add more milk by the 1/4-teaspoon, mixing to combine well, until the glaze falls off the spoon slowly, in a thick but pourable glaze. Add milk very slowly, as it is much easier to thin, than to thicken, the glaze. If you do thin the glaze too much, add more confectioners’ sugar a teaspoon at a time to thicken it. Drizzle the glaze in zigzag patterns all over the top of the cooled quick bread. Slice thickly and serve.