Preheat the oven to 375 degrees. Butter a 12-cup muffin pan.
In a medium bowl, whisk together the flour, baking powder and grated nutmeg.
In a small bowl, shake the flour over the blueberries.
In a large bowl, using an electric mixer, cream together the sugar and butter. Beat in the egg. With the mixer on low speed, add about half the flour mixture, half the milk, and then finish with the flour and the remaining milk.
Fold in the blueberries.
Portion the batter between the muffin cups and bake until a toothpick comes out clean, about 24 minutes. Let cool in the pan for 5 minutes, then transfer to a wire rack.
To finish the dirt bombs: In a medium bowl, combine the sugar and cinnamon. Pour the melted butter into another bowl.
Dip the tops of the muffins in the melted butter, then in the cinnamon sugar.