Heat oven to 325 F. Lightly spray sides of 9-inch springform pan. Cover the bottom with a round piece of parchment.
In a small bowl, combine graham cracker crumbs, sugar, and melted butter. Stir well.
Using a straight-sided cup, press crumb mixture firmly into prepared pan, covering the bottom and about halfway up the sides. Bake for 12 minutes, then move to a cooling rack.
Using a medium pot, combine berries and sugar. Heat on medium until mixture boils. Adjust the heat to achieve a low boil and cook for 3 minutes, stirring frequently.
In a small bowl, combine juice from one lemon, water, and cornstarch. Stir until combined and pour slowly into boiling mixture while stirring.
Continue to cook and stir until thick, about 2 minutes. To test thickness, use a spoon to scrape a line along the bottom of the pan; it should take a few seconds for the mixture to fill back in.
Remove from heat. Move 1/4 cup of the hot mixture to a shallow dish to cool quickly. Set the pan with the remaining sauce aside and stir occasionally.
In microwave (or small pan on low heat) combine the heavy cream and candy melts. Heat slowly until melted and smooth. Set aside.
In a large bowl, beat cream cheese until smooth. Add powdered sugar and beat well.
Add lemon zest, sour cream, and melted chocolate. Beat until combined.
Add the reserved 1/4 cup of berry mixture and the whipped topping, beating on low speed just until incorporated. Drop by large spoonfuls into pan. Spread gently, taking care not to disturb the crust.
Check the temperature of the remaining berry mixture. It can be warm, but if it’s hot, place pan in a larger pan of cold water to cool quickly. Spread over the cream cheese filling, cover, and place in freezer for at least 4 hours.
Allow the dessert to sit at room temperature for 10-15 minutes before serving. Decorate with whipping cream and berries if desired.