01 - Preheat oven to 325°F. Lightly grease a 9-inch springform pan and line base with parchment paper.
02 - Combine crushed graham crackers, melted butter, and sugar in a bowl. Press mixture evenly into pan base. Bake for 8 minutes, then set aside to cool slightly.
03 - Combine blackberries, sugar, and lemon juice in small saucepan. Cook over medium heat until berries break down and mixture thickens, 8-10 minutes, stirring frequently. Puree with hand blender, then strain through fine mesh sieve to remove seeds. Let cool.
04 - Using electric mixer, beat cream cheese and sugar until smooth and creamy. Add eggs one at a time, mixing well after each addition. Blend in sour cream, vanilla extract, and flour until just combined.
05 - Pour cheesecake filling over cooled crust. Dollop spoonfuls of blackberry puree over top, then swirl gently with skewer or knife for marbled effect.
06 - Place pan in larger tray filled with hot water to create water bath. Bake for 50-60 minutes until center is almost set but slightly wobbly.
07 - Turn off oven, crack door open, and let cheesecake cool slowly for 1 hour. Remove from oven and refrigerate for at least 4 hours or overnight before serving.
08 - Before serving, garnish with fresh blackberries, mint leaves, and whipped cream if desired.