1.Preheat oven to 350 degrees. Into a medium bowl, sift together flour, baking soda, baking powder, and salt. Butter a 9-inch square baking pan.

2. Prepare crumb topping. In a medium bowl, combine cinnamon, salt, Splenda® Brown Sugar Blend, and flour. Cut in the butter using your hands, two knives, or a pastry blender until well combined and crumbly. Set aside.

3. In the bowl of electric mixer fitted with the paddle attachment, cream butter and Splenda® Sugar Blend 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 the sour cream, and beat just until well combined. Fold in 2 cups blueberries. Spoon batter into prepared pan. Toss remaining cup blueberries with the crumb topping. Sprinkle crumb topping over cake. Bake until golden brown and cake tester comes out clean, 50 to 60 minutes.