Sauce

• In a small bowl: add blackberries, sugar and lemon juice. Let sit for 20 minutes. Use a fork/masher and smash until you release most of the liquid from the blackberries. Optional: use a food chopper or processor.
• Add cornstarch and mix everything together. Use a fine mesh to strain the liquid from the blackberries. Discard the blackberries solids. Freeze the sauce for 15-20 minutes.

Crust

• Preheat the oven to 325°F. Place parchment paper with overhanging edges on the bottom of the 9"x 9" pan (this will help when removing the crumble bar from the pan later). Grease the sides with cooking flour spray or butter.
• Use a food processor to crumble the Oreos. Add butter then continue to mix the Oreos. Then form the crumbs into the bottom of the pan (use the bottom of a measuring cup to help press down). Bake fro 10 minutes. Then, remove from the oven and let rest for 15 minutes.

Cheesecake

• In a medium size bowl: add softened cream cheese and sugar. Add 1 egg and whip until smooth. Continue to add the other egg and continue to whip until smooth. Whip until smooth. Add sour cream, vanilla extract, salt and whip until smooth. DO NOT OVERMIX.
• Pour the cheesecake batter into the pan. Spread and level the cream cheese mixture using a silicone or cake spatula. Then very gently jiggle the pan until settled and level (this will help it look nice and even across the top). 
• Drizzle the sauce over the top of the cheesecake (do not pour all the sauce directly on top in one spot). Use a toothpick to make cross cutting swirls to enhance presentation.
• Place the pan in the middle of the oven rack. Bake for 30-35 minutes (mine took ~30 minutes). 
• Remove the pan from the oven and let cool completely for at least 2 hours (to room temperature). Then, cover with plastic wrap and chill in the refrigerator for at least 6 hours or preferably overnight. Prior to serving, remove the cheesecake from the pan and then cut into 9 pieces. 

Serve & Enjoy!