01 - In a small bowl, combine chopped pecans, granulated sugar, cinnamon, and softened butter. Mix until crumbly and set aside.
02 - Preheat oven to 375°F (190°C). Grease a muffin tin or line with paper liners.
03 - In one bowl, whisk together flour, baking powder, and cinnamon. In a separate bowl, combine mashed sweet potato, sugar, vegetable oil, and eggs. Blend wet ingredients into dry ingredients until just incorporated.
04 - Evenly distribute the batter into the prepared muffin tin, filling each cup halfway.
05 - Sprinkle the streusel topping generously over each muffin.
06 - Bake for 20 to 25 minutes, or until a toothpick inserted into the center of a muffin comes out clean.