Add the blueberries, sugar, lemon juice, vanilla, and cornstarch to a medium pot. Cook over medium-low heat for 15 minutes until thick. Halfway through, smush some of the blueberries with the back of a wooden spoon. Remove from heat and allow to cool completely.

Preheat oven to 350 degrees. Grease a 9×9 pan and line it with parchment paper.

Add the butter, sugar, and vanilla to a medium bowl and cream together with an electric mixer on high speed until light and fluffy, about 2 minutes.

Add in the flour and salt and mix on low speed just until combined.

Tightly press the cookie crust mixture into the bottom of the prepared pan. Bake the crust for 10 minutes, then let cool.

In a large bowl, mix the cream cheese, sugar, and cornstarch together with a hand mixer on medium speed until smooth and free of lumps, about 2 minutes.

Add in the sour cream, vanilla, and lemon zest to the cream cheese mixture and mix on medium-low speed just until combined.

Add in the eggs and mix on medium-low speed just until combined.

Pour the cheesecake batter into the prepared baking pan with the crust. Spoon the blueberry jam on top and gently swirl with a butter knife.

Bake for 38-42 minutes. The center will have a slight jiggle. Then turn the oven off and prop the oven door open for 10 minutes using a wooden spoon.

Remove the cheesecake bars from the oven and allow them to cool completely in the pan on a wire rack. Cover and transfer to the fridge. Allow them to chill in the fridge for 6 hours, or until completely cold.

Once cold, carefully remove the cheesecake from the pan by pulling up on the parchment paper. Transfer to a serving plate or board and cut into 16 squares using a sharp knife.