Buttermilk Blueberry Casserole

1/2 c butter, softened
7/8 c sugar (or 3/4 c + 2 TBS)
1 egg, room temperature
1 tsp vanilla
2 c flour
2 tsp baking powder
1 tsp salt
2 c fresh blueberries
1/2 c buttermilk
1 TBS sugar (for sprinkling on top)

Preheat oven to 350 degrees.
Cream butter and 7/8 c sugar.
Add egg and vanilla and beat until combined.
Toss blueberries with 3/4 c of flour, then whisk in remaining flour.
Add flour mixture to batter, alternating with buttermilk.
Fold in blueberries.
Grease 9" baking pan (or something similar).
Spread batter into pan.
Sprinkle with remaining sugar.
Bake 35 to 45 minutes.
Let cool at least 15 minutes.