01 - Preheat oven to 325°F. Lightly grease a 9-inch springform pan and line bottom with parchment paper.
02 - Combine graham cracker crumbs, melted butter, and sugar in mixing bowl. Press mixture firmly onto bottom of prepared pan. Bake for 8 minutes, then set aside to cool.
03 - In small saucepan, combine blackberries, sugar, and lemon juice. Cook over medium heat until berries break down and mixture thickens, approximately 8-10 minutes, stirring frequently. Puree with immersion blender and strain through fine mesh sieve to remove seeds. Allow to cool completely.
04 - Using electric mixer, beat cream cheese and sugar until smooth and creamy, approximately 2-3 minutes. Add eggs one at a time, mixing well after each addition. Blend in sour cream, vanilla extract, and flour until just combined, taking care not to overmix.
05 - Pour cheesecake batter over cooled crust. Drop spoonfuls of blackberry puree across surface. Use skewer or knife to gently swirl puree through batter for marbled effect.
06 - Place springform pan inside larger roasting pan. Fill outer pan with hot water until halfway up springform pan sides. Bake for 50-60 minutes until center is almost set but still slightly wobbly when shaken.
07 - Turn off oven and crack door open slightly. Let cheesecake cool in oven for 1 hour. Remove from water bath and refrigerate for minimum 4 hours or preferably overnight before serving.
08 - Top with fresh blackberries, mint leaves, and dollops of whipped cream just before serving.