1/3 c. all-purpose flour
1/2 tsp. cinnamon
1/2 c. sugar
6 tbsp. butter, softened
1 3/4 c. all-purpose flour
1 1/2 c. fresh blueberries
1/2 c. sour cream
1/3 c. brown sugar
4 tbsp. butter, sliced
2 tsp. baking powder
Pinch of salt
1 lg. egg
1 tsp. vanilla extract
Heavy cream for serving

Preheat oven to 375 degrees. Butter an 8-inch baking dish.

Prepare the topping: In a small bowl, combine 1/3 cup flour, brown sugar, and cinnamon. Cut in 4 tablespoons butter to resemble coarse crumbs.

Prepare the batter: In a large bowl, beat 6 tablespoons butter until creamy. Gradually beat in the sugar until light and fluffy. Add the egg and vanilla and beat until smooth, then beat in the sour cream.

In a medium bowl, stir together the flour, baking powder, and salt to evenly blend. Quickly stir the dry ingredients into the butter mixture just to moisten; the batter will be thick and lumpy. Fold in rinsed and dried blueberries and turn into the prepared dish.

Crumble the reserved topping over the batter. Bake for 30-35 minutes, until toothpick inserted comes out clean. Cool on a rack for 15-20 minutes. Cut into 9-inch squares and serve warm with heavy cream.