Put 2 cups of blueberries and the sugar into a saucepan set over medium heat. Stir continuously until the sugar has dissolved. Simmer for 5 minutes or until the blueberries have started to break down.

Meanwhile, put the water, lemon juice, and cornstarch into a small bowl and whisk with a fork until the cornstarch has dissolved.

When the blueberries have broken down pour this cornstarch slurry into the saucepan and stir it in cooking for approximately 2 minutes. The sauce will thicken quickly and should look glossy and syrupy.

Remove the pan from the heat, stir in the remaining 1/2 cup of blueberries, and set it aside to cool before refrigerating.

Put the Graham Crackers into a food processor and blitz until fine crumbs. Add the sugar and melted butter and blitz again until you have the consistency of wet sand.

Line an 8-inch square baking pan with parchment paper. Pour the crumb mixture into the bottom of the pan and press it down into an even layer. Set aside.

Put the cream cheese and sugar into a large mixing bowl and beat until creamy.

Add the sour cream, vanilla extract, and lemon juice and beat until combined.

In a separate bowl beat the heavy whipping cream until it reaches stiff peaks. Add the whipped cream to the cream cheese mixture and fold everything together gently by hand.

Transfer the cheesecake filling on top of the Graham Cracker crust. Use an offset spatula to smooth the top. (If you don't have an offset spatula, use your fingertips.) Cover with cling wrap and put in the fridge to set for at least 4 hours but overnight is best.

When the cheesecake is set, use the parchment paper to lift it out of the baking pan.

Spoon the blueberry sauce over the top of the cheesecake.