In medium bowl, blend together butter, sugar, eggs, milk, and vanilla.
In large bowl, sift together flour, baking powder and salt.
Pour butter mixture into dry ingredients and mix well.
Fold blueberries into mixture carefully berries aren't crushed.
Spoon muffin mix into paper liners.
Bake for 25 to 30 minutes depending on how full the liners are, I like to overfill a little because the top of the muffin is my favorite part but it may take a little longer to cook depending on the oven.