Step 1: Preheat your oven to 375°F (190°C) and line a 12-cup muffin tin with paper liners or grease with non-stick spray.
Step 2: In a medium bowl, whisk together the flour, baking soda, baking powder, salt, cinnamon, and nutmeg until well combined.
Step 3: In a large bowl, whisk together the sweet potato puree, brown sugar, granulated sugar, oil, eggs, and vanilla extract until smooth.
Step 4: Gradually add the dry ingredients to the wet ingredients, stirring gently with a spatula until just combined. Fold in the 1/2 cup of chopped pecans.
Step 5: To make the streusel, combine the 1/2 cup chopped pecans, brown sugar, and flour in a small bowl. Cut in the cold butter using a fork or your fingers until the mixture resembles coarse crumbs.
Step 6: Divide the batter evenly among the muffin cups, filling each about three-quarters full. Generously sprinkle the pecan streusel over the top of each muffin.
Step 7: Bake for 22-25 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Step 8: Allow the muffins to cool in the tin for 5 minutes before transferring them to a wire rack to cool completely.