Preheat the oven to 375°F. Line a standard 12-cup muffin pan with paper liners.
Prepare the crumb topping: In a medium bowl, whisk together the flour, sugar, pecans, cinnamon, and salt. Add the melted butter and stir to combine. Set aside.
Prepare the muffins: In a medium bowl, whisk together the flour, baking powder, cinnamon, ginger, nutmeg, salt, and baking soda.
In a large bowl, with an electric mixer on medium speed, beat the butter and sugar until fluffy, about 3 minutes. Beat in the eggs one at a time. Beat in the mashed sweet potato. Beat in the flour mixture. Do not overmix.
Divide the batter evenly among the muffin cups. Sprinkle the crumb mixture evenly over the tops, squeezing it to create clumps of various sizes.
Bake the muffins until they are puffed and set and a toothpick inserted into the center of one comes out clean, 26 to 30 minutes. Let the muffins cool in the pan on a rack for 10 minutes, then transfer to the rack to cool completely.
