Grease eighteen 2-1/2-inch muffin cups or line with paper bake cups.
In a medium mixing bowl, stir together flour, the 2/3 cup sugar, baking powder, nutmeg, and salt. Make a well in the center of dry ingredients; set aside.
In another mixing bowl, beat eggs. Stir in milk, the 1/3 cup melted butter or margarine, and vanilla. Add all at once to dry ingredients. Stir just until moistened (batter should be lumpy). Fold in blueberries.
Spoon batter into prepared muffin cups, filling each 3/4 full. Bake in a 375 degree F oven for 20 to 25 minutes or until tops of muffins are golden.
Place pan of muffins on wire rack. Brush with additional melted butter or margarine; sprinkle with sugar. Remove from muffin cups. Serve warm. Makes 18 muffins.