1/2 c. (1 stick) unsalted butter (plus more for pan)
2 c. flour (plus more for pan)
1 1/2 tsp. baking powder
1/2 tsp. salt
3/4 c. sugar
1 egg
1 tsp. vanilla
1/2 c. milk
5 c. blueberries
1 recipe Streusel Topping (recipe follows)

Preheat oven to 350°F. Butter and flour spring-form baking pan; set aside. Sift together flour, baking powder and salt; set aside. With electric mixer on medium, cream butter and sugar until light and fluffy, about 3 minutes. Reduce speed to low and add egg and vanilla. Alternately add flour mixture and milk, beginning and ending with flour mixture. Fold in berries.

Pour batter into prepared pans; sprinkle Streusel Topping generously over batter.

Bake for 60 to 70 minutes at 350°F or until cake tests done. Remove from oven, leaving in pan for 10 minutes on a cooling rack. Remove from pan; let cool additional 15 minutes before serving.

Streusel Topping:

1 tsp. cinnamon
1/4 tsp. salt
1/4 c. light brown sugar
1 c. flour
6 tbsp. unsalted butter (room temperature)

In a medium bowl, mix dry ingredients together; cut in butter using a pastry blender or fork until fine crumbs form. Using hands, squeeze together most of the mixture to form large clumps. Sprinkle on top of cake before baking.