Preheat the oven to 350°F (175°C). Line the bottom of a 9-inch springform pan with parchment paper and lightly grease the sides.

In a large bowl, combine flour, baking powder, salt, brown sugar, granulated sugar, and lemon zest.

Add the cold butter and work it into the flour mixture using a pastry cutter, fork, mixer, or your fingertips until coarse crumbs form.

Add the eggs and vanilla extract, mixing until the dough becomes crumbly. If needed, squeeze portions together to create pea-sized crumbs.

Press about two-thirds of the crumb mixture firmly into the bottom and about 1½ inches up the sides of the prepared pan.

Refrigerate both the crust and the remaining crumb mixture while preparing the filling.

In another bowl, beat the cream cheese, mascarpone, sugar, vanilla, and cornstarch until just combined.

Add the eggs and mix gently until smooth. Avoid overmixing to keep the filling creamy.

Pour half of the filling into the chilled crust. Scatter about ⅔ cup of blueberries over the filling.

Spread the remaining cheesecake filling evenly over the berries.

Sprinkle the remaining blueberries across the top, then cover with the reserved crumb mixture.

Bake the Blueberry Cheesecake Crumb Cake for 65–75 minutes, or until the top is golden and the center is set. If the top browns too quickly, loosely cover it with aluminum foil.

Cool completely before removing the springform ring.

Mix the powdered sugar and milk until smooth. Drizzle over the cooled cake before serving.