The first five ingredients (wet) mix well. Add flour and baking powder, mix gently until ingredients are shallowly moistened. Do not over-stir!
Stir in blueberries, divide amount evenly among 12 muffin cups.
Bake at 200 °C for about 22-25 min. until muffins are light brown (stick test). Cool for 10 min, then remove from the pan. Cool. When cold, brush with frosting.
Frosting: stir ingredients until well blended.