Preheat oven to 325°F and grease a 9-inch springform pan.
In a small saucepan, melt the butter and the semisweet chocolate chips together over low heat. Set aside to cool.
In a mixing bowl, beat Norman's Kosher Cholov Yisroel Cream Cheese and granulated sugar with an electric mixer until smooth.
Add in flour, vanilla extract, and eggs, one at a time, and mix until just blended.
Mix in the cooled chocolate-butter mixture and the whiskey until just combined.
Stir in the unsweetened cocoa powder until just blended.
Sprinkle the pistachio crumbles evenly over the bottom of the greased pan.
Pour the cheesecake batter over the pistachio crust layer and smooth the surface with a spatula.
Bake for 60-65 minutes until the cheesecake is just set. Turn off the oven and allow the cheesecake to cool in the oven for an additional 30 minutes.
Remove the cheesecake from the oven and chill in the refrigerator for at least 4 hours, preferably overnight.
Before serving, combine mixed berries and heavy whipping cream in a bowl. Using an electric mixer, whisk on low until the cream begins to thicken. Increase the speed to high and gradually add in powdered sugar until soft peaks form.
Decorate the chilled cheesecake with the whipped cream mixture and additional mixed berries.