Make the topping
In a medium bowl, stir the flour, sugar, brown sugar, cinnamon, and salt until well blended. Add the melted butter and mix with a fork, stirring until the butter is absorbed and the dry ingredients are uniformly moistened. Set aside.
Make The Cake
Position a rack in the center of the oven and preheat the oven to 350 degrees F. Butter and flour the bottom and sides of a 9 or 10-inch springform pan OR a 9 inch square baking pan.
In a medium bowl, whisk together the flour, baking powder, baking soda, and salt until well blended.
In a small bowl, toss the blueberries with 1 tablespoon of the flour mixture until the berries are coated; set aside. In a small bowl, whisk together the sour cream and vanilla extract; set aside.
In a large bowl, beat together the butter and granulated sugar a medium speed until light and fluffy, about 3 or 4 minutes. Beat in the eggs one at a time, beating well after each addition and scraping down the sides of the bowl as necessary. At low-speed, beat in the flour mixture in three additions, alternating it with the sour cream in two additions. Using a rubber spatula, fold in the blueberries. Scrape the batter into the prepared pan and smooth the top with a spatula.
Sprinkle the crumb topping evenly over the batter, breaking up any large lumps with your fingers.
Bake the cake until a toothpick inserted into the center comes out clean, about 45 minutes. Place the cake in the pan on a wire rack to cool:
If baked in springform pan, cool on rack 20 minutes. Then unlatch springform and cool completely before serving.
If baked in square baking pan, cool completely and cut cake into squares, serving from the pan.