Preheat oven to 350 degrees.
Spray muffin pans (large size) with non-stick baking spray.
Mix the 2 last ingredients (sugar and grated nutmeg) together in a small bowl. Set aside.
Mix flour, baking powder and salt in a medium bowl and set aside.
Mix sour cream and vanilla in a measuring cup and set aside.
In a large bowl cream butter and sugar. Add one egg at a time incorporating the eggs well into the butter/sugar mixture. Add sour cream mixture. Mix well again.
Add flour and gently fold in until well incorporated. Do not over mix.
Add blueberries and gently fold into batter.
Distribute batter into muffin pans and sprinkle each with 1 teaspoon of sugar/nutmeg mixture.
Bake for 18-20 min. until golden on top. Add 5-10 min. when using frozen berries.
Let stand for 10 minutes before removing muffins from tins. Serve and enjoy!