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

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

Add the butter, sugar and vanilla to 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. Use a ¼ cup measuring cup to make this easier.

Bake the crust for 10 minutes, then let cool.

Preheat oven to 350 degrees if not still preheated from the crust.

In a large bowl, mix the cream cheese, sugar and cornstarch together with 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. Then cover and transfer them to the fridge. Allow them to chill in the fridge for 6 hours, or until completely cold.

Once the cheesecake is cold, pull up on the parchment paper to carefully remove the cheesecake from the pan. Transfer to a serving plate or board. Cut into 16 squares using a sharp knife.

Run the knife under hot water then wipe it with a towel each time you make a cut. This will allow you to make clean, pretty cuts.