Preheat the oven to 375°F. Lightly grease a standard 12-cup muffin tin; or line the tin with papers, and grease the papers., In a medium-sized bowl, beat together the butter and sugar until well combined., Add the eggs one at a time, scraping the sides and bottom of the bowl and beating well after each addition., Beat in the baking powder, salt, and vanilla., Add the flour alternately with the milk, beating gently just to combine. Scrape the bottom and sides of the bowl., Mash 1/2 cup of the blueberries. Add the mashed and whole berries to the batter, stirring just to combine and distribute., Scoop the batter by the heaping 1/4-cupful into the prepared muffin pan; a muffin scoop works well here., Sprinkle about 1 teaspoon granulated sugar atop each muffin, if desired. It's traditional — go for it!, Bake the muffins for about 30 minutes, until they're light golden brown on top, and a toothpick inserted into the middle of one of the center muffins comes out clean., Remove the muffins from the oven, loosen their edges from the pan, and after about 5 minutes transfer them to a rack to cool.