Preheat oven to 200 degrees C and line 12 muffin cups with paper muffin cups.
Cream the butter and sugar until light with an electric beater, about 3 minutes. Beat in the eggs one at a time. Sift together the flour, baking powder and salt then add to the butter alternately with the milk.
Toss the blueberries with the vanilla essence, then fold into the batter. Divide the batter between the muffin cups and bake 15 minutes.