Preheat oven to 375*. Spray a 9 inch round springform pan with cooking spray. I also line the bottom with parchment.
IN a bowl or food processor, combine flour, 1/2 cup sugar, baking powder, and salt. Cut in or process in butter until mixture resembles coarse crumbs. Stir or process in the egg and vanilla. Press lightly into the bottom of the prepared pan.
Sprinkle cornstarch over the blueberries and gently stir until cornstarch disappears. Spread the blueberries over the crust.
Stir sour cream, 1/2 cup sugar, egg yolks, and vanilla together. Pour this mixture over the blueberries and carefully spread it across the top.
Set the springform pan on a foil lined cookie sheet and bake for 60-70 minutes, until the top is lightly browned around the edges. The center will still be a little loose, but it will set as it cools. Loosen the edges with a knife while it's still hot, but don't remove the sides of the springform just yet. Cool and chill completely for several hours. Remove springform. Serve each slice with whipped cream.