1. Preheat oven to 325 degrees F. Brush a 6 3/4-by-4 1/4-by-2 3/4-inch loaf pan with oil; set aside.
2. In a large bowl, whisk together flour, potato starch, arrowroot, 1 cup sugar, baking powder, baking soda, salt, xanthan gum, and 1 tablespoon cinnamon.
3. In a medium bowl, stir together oil, applesauce, and 1 cup hot water. Add oil mixture to flour mixture; stir until well combined. Measure out 1/3 cup of batter and place in a small bowl. Pour remaining batter into prepared loaf pan. Stir remaining 1/4 cup sugar and 1 tablespoon cinnamon into reserved batter. Add to loaf pan, swirling to combine.
4. Transfer to oven and bake about 20 minutes. Brush top of loaf with oil and continue baking until golden brown, about 15 minutes. Let cool completely on a wire rack before unmolding.
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