In a medium bowl, mix together all-purpose flour, dark brown sugar, granulated sugar, and cinnamon until evenly combined. Add room temperature butter and use your fingers or a pastry cutter to blend the mixture until it resembles coarse crumbs. Set this crumble mixture aside.

Preheat your oven to 350°F (175°C) and prepare a 9-inch springform pan by greasing it lightly with butter and lining the bottom with parchment paper.

In a large mixing bowl, whisk together the all-purpose flour, baking powder, and salt until well combined.

Using a stand mixer or a large bowl and hand mixer, beat softened butter and granulated sugar together until light and fluffy, about 3-4 minutes. Add eggs, one at a time, mixing well after each addition. Incorporate half of the dry ingredients followed by sour cream, vegetable oil, lemon zest, and vanilla extract; finally, stir in the remaining dry ingredients until just combined.

Toss blueberries in cornstarch and gently fold half into the batter. Pour the batter into the prepared pan, spreading it evenly. Top with remaining blueberries and sprinkle the crumble mixture on top.

Bake for 45-50 minutes, or until a cake tester comes out clean. Allow the cake to cool in the pan on a wire rack for 10-15 minutes before removing the sides.

In a small bowl, whisk together sifted powdered sugar, lemon juice, vanilla extract, and sour cream until smooth. Drizzle generously over the cooled cake.