In a saucepan, add strawberries that are cut in quarters, add the sugar, and lemon juice, and mix over medium-high heat.
Decrease the heat to medium-low and simmer for 20 minutes mixing occasionally.
Mix the cornstarch in a small bowl with a little bit of water and pour it into the strawberry mixture mixing constantly. Simmer for another 2-3 minutes until the mixture thickens.
Set aside and let it cool while you make the cheesecake crust and filling.
Prepare a 9-inch springform pan with parchment paper, and preheat an oven to 180c (350f). Pulse graham crackers or digestive biscuits in a food processor until fine crumbs form. If you don’t have a food processor on hand, place the crackers in a Ziplock bag and smash them with a cup until fine crumbs form. Into a small to medium mixing bowl, add the crumbs, and melted butter. Mix with a spoon until the crumbs are coated with butter. Transfer the crumbs into a prepared 9-inch springform pan, pressing evenly and firmly into the pan.
Bake the crust in a 180c (350f) preheated oven for 8 minutes. Keep an eye on the crust and make sure it doesn’t burn. Take the crust out of the oven and let it cool to room temperature.
In a large mixing bowl, add the room-temperature cream cheese, granulated sugar, lemon zest, lemon juice, sour cream, and vanilla extract, and mix with an electric hand mixer until is creamy. Whisk the eggs in a small bowl add them to the cheesecake mixture and mix until the mixture is smooth. Sift the cornstarch into the mixture and mix until combined and there are no lumps of cornstarch showing. Scrape down the sides of the bowl to ensure there are no lumps of cream cheese or unmixed batter. Pour the cheesecake batter over the crust, and release air bubbles by gently tapping the pan onto a flat surface.
Top the cheesecake batter with dollops of the strawberry sauce, and use a toothpick or a butter knife to make swirls.
Bake it in a 140c (280f) preheated oven for about an hour or until the edges of the cheesecake are set, but the middle is a bit jiggly.
Open the oven door halfway, and let the cheesecake cool to room temperature for 1-2 hours.
After the cheesecake is cooled, wrap the cheesecake with plastic wrap tightly, and place the cheesecake in the fridge to cool completely for at least 5 hours.
Make the whipped cream. In a large mixing bowl, add the cold heavy cream, vanilla extract, and powdered sugar. Whip with an electric hand mixer or in a stand mixer with the balloon attachment to stiff peaks.
Transfer the whipped cream to a pastry bag fitted with a star piping tip and pipe dollops of whipped cream around the edges of the cake. Top it with more sliced strawberries if desired and serve.