Preheat your oven to 175ºC (350ºF) and prepare a 9-inch springform pan by lining the bottom with parchment paper.

In a medium bowl, combine the crumble ingredients until it resembles coarse crumbs, about 5 minutes. Set aside.

In a large bowl, cream the butter and granulated sugar until light and fluffy, about 3 minutes. Add eggs one at a time, mixing well after each.

Gradually add half of the dry ingredients, then stir in lemon zest, sour cream, vegetable oil, and vanilla.

Mix in the remaining dry ingredients until just combined. Toss blueberries with cornstarch and fold half into the batter.

Pour batter into the pan, smoothing the top, and sprinkle remaining blueberries and crumble topping.

Bake for 45-50 minutes, checking doneness with a toothpick.

Once done, cool in the pan for 10 minutes before transferring to a wire rack.

Prepare the lemon glaze by mixing powdered sugar and lemon juice until smooth.

Drizzle glaze over the cooled cake, let set for a few minutes, then slice and serve.