Step 1: Preheat your oven to 350°F (175°C) and grease a 9x5 inch loaf pan.
Step 2: In a medium bowl, whisk together the flour, baking soda, baking powder, salt, and 1 teaspoon of cinnamon.
Step 3: In a large bowl, beat the sweet potato puree, oil, eggs, and granulated sugar until well combined and smooth.
Step 4: Gradually add the dry ingredients to the wet ingredients, stirring until just combined. Do not overmix.
Step 5: In a small bowl, mix the 1/2 cup brown sugar and 1 tablespoon cinnamon to create the swirl mixture.
Step 6: Pour half of the batter into the prepared loaf pan. Sprinkle 2/3 of the cinnamon sugar mixture over the batter.
Step 7: Top with the remaining batter, then sprinkle the remaining cinnamon sugar on top. Use a knife to swirl the layers gently.
Step 8: Bake for 60-70 minutes, or until a toothpick inserted into the center comes out clean.
Step 9: Allow the bread to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.