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 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, 8-10 minutes. Puree and strain through sieve. Let cool.
04 - Using mixer, beat cream cheese and sugar until smooth. Add eggs one at a time, mixing well after each. Blend in sour cream, vanilla, and flour until just combined.
05 - Pour filling over cooled crust. Dollop spoonfuls of blackberry puree over top, then swirl gently with skewer or knife for marbled effect.
06 - Bake in water bath (place pan in larger tray with hot water) for 50-60 minutes until center is almost set but slightly wobbly.
07 - Turn off oven, crack door open, and cool 1 hour. Remove from oven and refrigerate at least 4 hours or overnight before serving.
08 - Garnish with fresh blackberries, mint leaves, and whipped cream if desired before serving.