Step 1: Make the blackberry swirl. Add the blackberries, sugar and lemon juice to a medium saucepan. Cook over medium heat, stirring frequently, until the berries begin to soften and release their juices. Once the berries are very soft, start mashing them (I use a potato masher for this!). Once the berries have released all their juices and are completely mashed, add the cornstarch and cook, stirring constantly, for another 60 seconds. This process takes about 8 to 10 minutes. Pour through a fine mesh sieve set over a heatproof bowl, pushing the mixture through and scraping the bottom of the sieve so that you get all the juices. Set the syrup aside to cool; discard the pulp.

Step 2: Make the crumb crust. Preheat the oven to 350°F. Spray a 9×13″ baking pan with non-stick spray and line with parchment paper, leaving an overhang on the two long sides of the pan. Place the cookie crumbs, sugar, and melted butter in a medium bowl and stir to combine. Press the mixture firmly into an even layer in the bottom of the prepared pan. Bake until lightly toasted and fragrant, 9 to 11 minutes. Set aside to cool.

Step 3: Make the cream cheese filling. Reduce the oven temperature to 325°F. Using an electric hand mixer or stand mixer fitted with the paddle attachment, beat the cream cheese until the blocks are blended together. Scrape down the sides and bottom of the bowl. Add the sugar and mix at high speed for 5 minutes, stopping to scrape down the sides and bottom of the bowl halfway through and again at the end.

Next add the sour cream, vanilla, lemon juice and salt and mix on medium speed until combined. Scrape down once more. Gradually add the eggs, one at a time, mixing on low speed until each egg is just incorporated into the batter. Be careful not to overmix once the eggs have been added, as this increases the chance of cracking.

Step 4: Layer the elements. Pour the cream cheese filling over the cooled crust and gently smooth into an even layer. Tap the pan on the counter a few times to release any air bubbles. Spoon the blackberry syrup in small dots all over the surface of the filling (you might not use all of it), then gently run the tip of a toothpick, wooden skewer or dinner knife over the surface to create a swirl pattern.

Step 5: Bake. Bake for 34 to 38 minutes, until the edges are set and slightly puffed and the center is almost set but maintains a slight jiggle (TIP: you want the center to jiggle like Jell-O, not slosh like water). Be careful not to overbake. Set aside to cool completely.

Step 6: Chill. Once cooled, cover with plastic wrap or foil and place in the fridge to chill for at least 8 hours, ideally overnight. Use the parchment paper handles to remove the chilled cheesecake from the pan before slicing into bars and serving.