01 - Preheat oven to 325°F. Lightly grease a 9-inch springform pan and line base with parchment paper.
02 - Mix crushed graham crackers, melted butter, and sugar in a bowl. Press evenly into pan base. Bake for 8 minutes, then set aside to cool.
03 - Combine blackberries, sugar, and lemon juice in a small saucepan. Cook over medium heat for 8-10 minutes until berries break down and mixture thickens, stirring frequently. Puree with hand blender and strain through fine mesh sieve. Cool completely.
04 - Beat cream cheese and sugar with mixer 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 the top, then swirl gently with a skewer or knife for a marbled effect.
06 - Place pan in a larger tray filled with hot water to create a 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 at least 4 hours or overnight before serving.
08 - Top with fresh blackberries, mint leaves, and whipped cream if desired before serving.