Sift dry ingredients together in a large bowl. In another bowl, whisk eggs, buttermilk, butter or oil, lemon juice and vanilla. Make a well in the dry ingredients and pour in liquid ingredients, mixing quickly.
Fold in blueberries. Spoon batter into greased muffin cups, almost to the top of each cup, and bake for 20 -30 minutes, or until golden brown. Wait a few minutes and then transfer muffins to a wire rack to cool.
In a small bowl, whisk powdered sugar and lemon juice until it is the consistency of thin icing. Brush each muffin top with about 1 tsp. of the glaze.