Preheat the oven to 375°F. Lightly grease a standard 12-cup muffin tin, or line the tin with papers, and grease the papers. (This will make 12 large muffins. Alternately, this recipe can make 18 medium sized muffins or 12 medium plus 12 mini, whatever you prefer)
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.
Add the blueberries to the batter, stir just to combine and distribute.
Scoop the batter into the prepared muffin pan(s). I love using a muffin scoop for this step.
Bake 12 full size blueberry muffins for approximately 25-30 minutes (bake medium sized muffins 20-25 minutes and minis for 15-20 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 5 minutes transfer them to a rack to cool. Serve with a pat of butter and enjoy!