This blueberry muffin recipe, from “Martha’s Entertaining,” features two options for topping: You could always try both, but if you plan on making the crumb topping, prepare that first. Alternatively, sprinkle granulated sugar and freshly grated mace, an aromatic spice made from the outer webbed shell of a nutmeg, over the batter just before baking.
http://www.marthastewart.com/965985/blueberry-muffins