Prepare the Crust: Combine crushed biscuits with melted butter and press into a pan. Chill to set.
Create the Pistachio Layer: Blend ground pistachios, sugar, and heavy cream until smooth, then spread over the crust.
Mix the Cream Cheese Filling: Beat cream cheese, sugar, and vanilla, then spread over the pistachio layer.
Make the Blackberry Topping: Cook blackberries with sugar, lemon juice, and cornstarch until thickened. Cool and spread over the cream cheese layer.
Chill & Garnish: Let the bars set in the refrigerator, then sprinkle with chopped pistachios and fresh blackberries before serving.