1 1/2 tsp. ground cinnamon
1/2 tsp. salt
1/2 c. (packed) light brown sugar
12 T. (1 1/2 sticks) unsalted butter, room temp.
2 1/2 c. plus 2 T. flour
1 tsp. baking soda
1 tsp. baking powder
1/4 tsp. salt
10 T. (1 1/4 sticks) unsalted butter, room temp.
1 c. sugar
3 large eggs
1 tsp. pure vanilla extract
1 1/4 c. sour cream
3 c. blueberries
CRUMB TOPPING: Toss blueberries with 2 tablespoons flour and set aside.
In a medium bowl, combine cinnamon, salt, sugar, and flour. Cut in the butter with your hands, two knives, or a pastry blender until well-combined and crumbly. Carefully fold in 1 cup blueberries.
CAKE: Preheat oven to 350 degrees. Sift together flour, baking soda, baking powder, and salt into a bowl; set aside.
Butter a 9 inch square baking pan. In an electric mixer, cream butter and sugar until light and fluffy, about 4 minutes. Add eggs one at a time until well combined. Add vanilla and beat until combined. Add reserved flour mixture and sour cream, beating until just well combined. Fold in 2 cups of blueberries.
Spoon the batter into prepared pan. Sprinkle crumb topping over cake. Bake until golden brown and cake tester comes out clean, approx. 50 to 60 minutes. Dust with powdered sugar.