Preheat oven to 375F.
With paper liners, line 18 muffin-pan cups (2-1/2 by 1-1/4 inches), or grease them well.
Sift flour with baking powder and salt.
Set aside.
In large bowl, with electric mixer at high speed, beat butter with granulated sugar, eggs, vanilla until light and fluffy—about 4 minutes—occasion- ally scraping side of bowl and beaters with rubber scraper.
At low speed, beat in flour mixture (in fourths) alternately with milk (in thirds), beginning and ending with flour mixture.
Beat just until smooth.
With rubber scraper, gently fold in blueberries just until combined.
Scoop about 1/4 cup batter into each prepared muffin cup, to fill each about two thirds full.
Bake 20 to 25 minutes, or until golden-brown and cake tester inserted in center comes out clean.
Remove muffins to wire rack; let cool slightly.
Serve warm or cold, sprinkled with confection- ers' sugar.
Makes 18 muffins.