Begin by crushing the digestive biscuits into fine crumbs, then combine them with melted unsalted butter in a mixing bowl. Stir until the crumbs are well-coated and form a sandy texture. Gently press this mixture into the bottom of an 8x8 inch lined baking pan, ensuring it's evenly packed. Chill the base in the refrigerator for about 20 minutes while you prepare the pistachio layer.

In a blender, add finely ground pistachios, 1/4 cup confectioners' sugar, and 1/4 cup heavy cream. Blend the ingredients on high speed until the mixture is smooth and creamy, resembling a thick batter. Once the biscuit base is set, spread the pistachio mixture evenly over it using a spatula. Place the pan back in the refrigerator for another 20 minutes to help the layer set perfectly.

Now, in a separate bowl, beat 1 cup of softened cream cheese with 1/2 cup of confectioners' sugar and 1 teaspoon of vanilla extract using an electric mixer until the mixture is light and fluffy. Once smooth, carefully spread this cream cheese mixture over the pistachio layer, making sure it's evenly distributed, and chill in the refrigerator again.

To make the tangy blackberry compote, place 2 cups of fresh blackberries, 1/2 cup of granulated sugar, 1 tablespoon of lemon juice, and 2 teaspoons of cornstarch into a saucepan over medium heat. Stir the mixture gently until the blackberries begin to break down and the compote thickens, usually about 5-7 minutes. Once thickened, remove from heat and let cool slightly before layering it over the cream cheese.

Once the blackberry compote has cooled, pour it evenly over the cream cheese layer. Use a spatula to ensure it spreads uniformly and covers all edges. After layering, return your baking pan to the refrigerator for at least 2 hours or until fully set.

When ready to serve, remove the bars from the refrigerator and carefully lift them out of the pan using the parchment paper. Slice into squares and sprinkle with 1/4 cup of chopped pistachios for added crunch. Enhance the presentation with a few fresh blackberries on top. Serve these decadent Blackberry Pistachio Dream Bars chilled.