• Preheat your oven to 350°F (175°C). Grease a 9-inch springform pan and line the bottom with parchment paper.

For the Crumble Topping:

• In a bowl, combine 1/2 cup flour and 1/2 cup granulated sugar. Add the cold, cubed butter and mix with your fingertips until the mixture resembles coarse crumbs. Set aside.

For the Cake:

• In another bowl, whisk together 1 1/2 cups flour, baking powder, baking soda, and salt. In a separate large mixing bowl, beat the softened butter and 2/3 cup granulated sugar until light and fluffy, about 3 minutes.
• Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract, lemon zest, and lemon juice until well combined. Gradually mix in the dry ingredients, alternating with sour cream, starting and ending with the dry ingredients.
• Gently fold in the blueberries and pour the batter into the prepared pan. Sprinkle the crumble topping evenly over the batter.
• Place the pan on a baking sheet and bake in the preheated oven for 45 minutes or until a toothpick inserted into the center comes out clean with just a few moist crumbs.
• Allow the cake to cool in the pan on a wire rack for 15 minutes. Then remove the springform ring and let cool completely before serving.