Preheat the oven to 350°F. Line the bottom of a 9-inch springform pan parchment paper. If your springform pan tends to leak, wrap the bottom in foil before baking.

In a large mixing bowl, whisk together the flour, granulated sugar, cornstarch, baking powder, salt, and lemon zest until evenly combined.

Using a hand mixer, mix in the olive oil on low speed. The mixture should look like damp, clumpy sand.

Mix in the eggs and vanilla extract on low speed until combined. Slowly stream in the buttermilk while mixing until the batter is smooth, glossy, and lump-free. Scrape down the sides and bottom of the bowl with a rubber spatula as needed.

In a separate bowl, stir together the frozen wild blueberries, brown sugar, and lemon zest until combined. You can also mix the blueberry topping directly in the prepared springform.

Spread the blueberry mixture evenly across the bottom of the prepared pan. Pour the cake batter over the blueberries and gently spread it into an even layer so the berries stay underneath.

Bake for 30-40 minutes, or until the top is golden and a toothpick inserted into the center comes out clean or with a few moist crumbs. The moisture from the blueberries can slow down baking, so if the top starts browning too quickly before the center is fully baked, loosely tent the cake with foil for the remaining bake time.

Let the cake cool in the pan for 10 minutes. Run a knife around the edge of the pan, then carefully release and remove the springform ring. Place a wire rack or serving plate over the top of the cake, then quickly and carefully flip it. Lift off the pan base and gently peel away the parchment paper. Let the cake cool completely, about 1 hour.

Slice and serve the cake with whipped cream, ice cream, or a dusting of powdered sugar.