1. Preheat oven to 375 derees F. Grease fifteen 2-1/2-inch muffin cups or line with paper bake cups; set aside.
2. In a medium bowl, stir together flour, the 2/3 cup sugar, the baking powder, nutmeg, and salt. Make a well in the center of flour mixture; set aside.
3. In a small bowl, beat eggs. Stir in milk, the 1/3 cup melted butter, and vanilla. Add egg mixture all at once to flour mixture. Stir mixture just until moistened (batter should be lumpy). Gently fold in blueberries.
4. Spoon batter into prepared muffin cups, filling each three-fourths full. Bake for 20 to 25 minutes or until tops of muffins are golden brown.
5. Place muffin pans on wire racks. Brush tops of muffins with additional melted butter; sprinkle with coarse sugar. Remove muffins from cups. Serve warm. Makes 15 muffins.
6. Make-Ahead Tip: Prepare and bake the muffins; cool. Place in an airtight container and freeze for up to 3 months. Thaw the muffins, covered, at room temperature. Wrap the muffins in foil and bake in a 350 degree F oven about 10 minutes or until heated through.