Start by crushing the digestive biscuits in a food processor until they reach a fine crumb texture without turning to powder. In a mixing bowl, combine the crushed biscuits with ground pistachios, ensuring they are evenly mixed. Press this mixture firmly into the bottom of a lined square baking dish to form a solid base, and then place it in the refrigerator for about 15 minutes to firm up.

In a clean food processor, combine the ground pistachios, heavy cream, and sugar, pulsing until the mixture is completely smooth and creamy. Make sure to check the consistency; it should be spreadable yet thick. Once ready, remove the base from the fridge and evenly spread the pistachio mixture over it, smoothing with a spatula for a nice, even layer. Return to the fridge for another 15-20 minutes.

In a mixing bowl, beat the cream cheese until it’s smooth and creamy, making sure there are no lumps. Gradually incorporate the chilled pistachio mixture into the cream cheese, blending well until homogeneous. Once combined, gently pour this luscious cream cheese layer over the chilled pistachio layer, ensuring it covers the entire surface. Chill again for approximately 15-20 minutes to set.

In a small saucepan over medium heat, combine the fresh blackberries with sugar and cornstarch. Cook gently, stirring often, until the mixture thickens and becomes bubbly, about 5-7 minutes. Remove from the heat and allow it to cool slightly before gently spooning it over the cream cheese layer. Spread evenly to ensure every bite is bursting with flavor, then return the dish to the refrigerator.

Cover the assembled Blackberry Pistachio Dream Bars with plastic wrap, ensuring it’s tightly sealed to prevent odor absorption. Let the bars rest in the refrigerator overnight; allowing this time enhances the flavors and helps the layers meld beautifully.

When you're ready to serve, take a sharp knife and dip it in warm water, which will help slice through the layers smoothly. Cut the bars into squares, making them easy to enjoy. Serve chilled for that delightful creamy texture.