• Combine the graham cracker baking crumbs and melted butter until moistened and crumbly.
• Press the mixture into the bottom of a 9-inch springform pan and refrigerate to set.
• Combine the cream cheese and powdered sugar in a large bowl, mixing with a hand mixer on medium speed (or in your stand mixer) until smooth. 
• Add the lemon juice and lemon zest and mix well until incorporated, scraping down the sides of the bowl to ensure everything is incorporated and distributed evenly.
• Fold in the whipped cream or whipped topping by hand until the mixture is fluffy and creamy and there are no streaks in the batter.
• Add the mashed blackberries and fold them in gently until the blackberries are streaked throughout the batter.
• Pour the cheesecake mixture into the prepared crust and smooth out the top with a rubber spatula or offset spatula.
• Refrigerate to set for 6 hours or overnight, or set in the fridge for 2-3 hours and then in the freezer for 2-3 hours before serving. OR, set in the freezer only for 3-4 hours.

For serving:

• Top with whipped cream or whipped topping and some fresh blackberries for garnish (optional).