Preheat oven to 350ºF. Grease and flour a 24-serving *mini muffin pan.
In a medium bowl, whisk together flour, baking powder, salt, cinnamon, ginger and nutmeg.
In a large bowl, beat sugar, oil, egg and pumpkin purée until smooth.
Stir in flour mixture just until combined. A few lumps are okay. Batter will be thick.
Transfer batter to prepared pan, about a scant 2 tablespoons of batter in each muffin cup.
Bake until toothpick inserted into muffins comes out clean, about 11-13 minutes. Do not over bake! Be diligent, since over baking can happen very quickly with mini muffins.
Let muffins cool in pan for 5 minutes. Turn muffins out onto a cooling rack.
Topping
Combine sugar and cinnamon in a shallow bowl.
Dunk warm muffins in melted butter, then roll in cinnamon sugar.