Step 1: Preheat your oven to 350°F (175°C) and grease a 9×5 inch loaf pan with butter or non-stick cooking spray.
Step 2: In a large bowl, whisk together the sweet potato puree, vegetable oil, 1/2 cup granulated sugar, light brown sugar, eggs, and vanilla extract until smooth.
Step 3: In a separate medium bowl, sift together the flour, baking soda, baking powder, salt, and 1 tablespoon of cinnamon.
Step 4: Gradually add the dry ingredients to the wet ingredients, stirring gently with a spatula until just combined. Do not overmix.
Step 5: In a small bowl, prepare the swirl mixture by combining the 1/4 cup sugar, 2 tablespoons cinnamon, and melted butter into a thick paste.
Step 6: Pour half of the sweet potato batter into the prepared loaf pan and spread it evenly.
Step 7: Drop spoonfuls of the cinnamon swirl mixture over the batter, then cover with the remaining sweet potato batter.
Step 8: Use a knife to gently swirl the layers together in a zigzag motion to create the cinnamon pattern.
Step 9: Bake for 55-65 minutes, or until a toothpick inserted into the center comes out clean.
Step 10: Allow the bread to cool in the pan for 15 minutes before transferring it to a wire rack to cool completely.