01 - Preheat oven to 350°F. Grease and flour a 9-inch round or square baking pan.
02 - In a bowl, combine flour, sugar, salt, and lemon zest. Add cold butter and use your fingers or a pastry cutter to rub until mixture resembles coarse crumbs. Refrigerate until needed.
03 - Whisk together flour, baking powder, baking soda, and salt in a medium bowl.
04 - In a large bowl, cream together butter and sugar until light and fluffy. Beat in eggs one at a time, then add lemon zest, lemon juice, and vanilla extract.
05 - Mix in half of the flour mixture, followed by the sour cream, then the remaining flour mixture. Stir until just combined.
06 - Gently fold in the blueberries, being careful not to overmix.
07 - Spread batter evenly in the prepared pan. Sprinkle the crumble topping evenly over the batter.
08 - Bake for 40 to 45 minutes, or until a toothpick inserted into the center comes out clean.
09 - Cool the cake in the pan for at least 20 minutes. For the glaze, whisk together powdered sugar and lemon juice until smooth, then drizzle over the cooled cake if desired.
10 - Slice and serve.