Place chocolate graham crackers, melted butter and sugar in bowl of food processor and blend until combined. Pour into 8x8 pan and press down firmly, making sure it is even.
Melt semi sweet chocolate in microwave. Place in small, microwave-safe bowl, 30 seconds at a time until there are no large pieces. Small pieces are ok, stir until completely melted and smooth. Pour on top of crust, spreading evenly.
Place in refrigerator for 15 - 20 minutes to set.
In a small pot, combine blueberries, sugar and lemon juice. Bring to a boil and cook until blueberries begin to burst and some of the liquid has evaporated, about 20 minutes. Stir occasionally. Remove from heat and cool.
Purée using an immersion blender or regular blender.
Using a hand mixer, beat cream cheese, sour cream and powdered sugar until smooth. Add COLD heavy cream and vanilla, beat until smooth and fluffy (3 - 4 minutes). Pour into pan and smooth top.
Dollop fresh blueberry sauce on top and using a butter knife, swirl sauce into cheesecake filling. Cover with plastic wrap and refrigerate at least 3 hours before serving.