To prepare the blueberry purée, place the blueberries into a blender or food processor fitted with a metal blade and completely purée. Strain into a small saucepan. Add the sugar and lemon juice and stir.
Place the saucepan on the stove top over high heat and bring to a boil. Reduce heat to medium and cook uncovered, stirring occasionally, for 7 to 10 minutes or until thickened. Transfer the mixture to a medium bowl. To use immediately, place that bowl in a larger bowl of ice cubes and water, sitting on top of the ice cubes. Let cool for 5 minutes and then it is ready to use. May be made four days in advance and stored in the fridge. To use the next day or later, allow to cool and then place into the refrigerator.
To make the shortbread cookies, grease an 8-inch square pan, line with parchment and then grease the top of the parchment.
Cut the butter into tablespoons and let sit at room temperature for 20 minutes. In the bowl of a stand mixer fitted with the paddle attachment, beat the butter. Scrape down the bowl and add the confectioners’ sugar, flour and salt, and beat on medium speed for two minutes or until the dough comes together.
Place the dough into the lined pan and press into an even layer. Freeze for 30 minutes or refrigerate overnight. Preheat oven to 300°F. Use a fork to score holes 1 1/4 to 1 1/2 inches apart across the top of the dough. Bake for 45 to 50 minutes, or until golden. Cool for 5 minutes on a wire rack and cut into bars or squares. Let cool for another 30 minutes. May be made five days in advance or frozen. You will not need all off the cookies for the cheesecake; weigh 8 ounces and set aside for the cheesecake crust and enjoy then rest!
To prepare the cheesecake, you will need a 9-inch springform pan. Trace the bottom of the pan on parchment paper and cut out the circle. Cover the top of the pan bottom with a 20-inch long piece of heavy-duty aluminum foil and then wrap the foil under the bottom of the bottom of the pan. Attach the pan sides to the bottom, lock it in place and then unwrap the foil and wrap it up and around the sides of the pan. (This will keep water from seeping into the cheesecake while it’s baking in a water bath.) Rub 1 tablespoon of butter around the bottom and sides of the pan. Press the parchment circle into the bottom of the pan and grease the top of the circle. Set aside a large roasting pan with sides taller than 2 inches high.
To make the crust, melt the remaining four tablespoons butter in a medium bowl. Crumble 8 ounces of the cookies into the bowl of a food processor fitted with a metal blade. Process until ground, leave some ¼-inch pieces. Transfer to the bowl and stir into the butter. Spoon mixture into the pan and press to cover the bottom of the pan. You can use a piece of parchment paper to help press the crumbs evenly while keeping your hands clean. Set aside.
To bake the cheesecake, preheat oven to 325°F (160°C). In a small bowl, mix sugar and lemon zest; I like to use my fingers. Place the eggs, cream cheese, sugar- lemon zest mixture, lemon juice, and cornstarch/flour into the bowl of a stand mixer or blender and beat on medium-high speed until smooth, scraping down the bowl as needed. The mixture should be entirely smooth.
Add 1/4 cup of the blueberry purée and blend until combined. Pour out2 1/4 cups of cheesecake filling into a measuring cup or bowl and set aside.
Add 7 tablespoons of the blueberry purée to the blender and remaining 1 tablespoon of cornstarch, and blend just until combined. Scrape down the sides so that all of the purée is mixed in.
Pour the darker purple cheesecake filling from the blender on top of the crust. Pour the reserved lighter-colored purple cheesecake filling on top.
Place the pan into the larger roasting pan and place it on the middle rack of the oven. Pour boiling water into the roasting pan, around the cheesecake pan, until the water reaches one-third to halfway up the sides of the cheesecake pan.
Bake the cheesecake for 1 hour and 10 minutes. Turn off the oven and prop the door open with a wooden spoon. Leave the cheesecake in the oven for another hour. Carefully remove the cheesecake pan from the roasting pan and let it sit on a wire rack until the cheesecake is completely cool. Refrigerate it for at least five hours or overnight.
To serve, pour half of the remaining blueberry purée over the top and garnish with fresh blueberries. Serve each slice with more blueberry purée and berries.
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