• First things first, let's get that oven nice and warm at 350°F (that's 180°C). Grab your 8x8 inch square pan and line it with parchment paper, leaving a good bit hanging over the sides. That overhang will be our handle later!

Making the Graham Cracker Crust

• Pop your graham crackers into the food processor. Give it a few pulses until they look like fine little crumbs. Now, add in your pistachios, brown sugar, cinnamon, nutmeg, and a touch of salt. Just a few more pulses to mix those dry ingredients.
• Pour in your melted butter and pulse once more until everything looks evenly moistened. Take that lovely crumb mixture and press it firmly and evenly into the bottom of your prepared pan.
• Bake this crust in the warm oven until the edges are just starting to turn golden—that should take about 10 to 12 minutes. Take it out and set it aside to cool, but keep the oven on!

The Creamy Filling

• In a bowl, let's combine the cream cheese, white sugar, cornstarch, salt, and nutmeg. Use your electric mixer to beat them until they are smooth and lovely, about 1 to 2 minutes.
• Next, beat in the vanilla, almond extract, and lemon juice until everything is combined. Pour in the heavy cream and mix until that, too, is smooth.
• Finally, add the egg and mix it in on a low speed, just until it's barely incorporated. We don't want to over-beat the eggs!
• Now, scoop out about 1 and 1/4 cups of that cream cheese filling into a separate bowl. To that smaller batch, add the pistachio butter and beat it until the color is uniform and beautiful.
• Pour this pistachio filling right over the cooled crust and spread it out gently into an even layer.
• Now, take the rest of your plain cream cheese filling and gently dollop it over the pistachio layer. Careful now! Gently spread this layer to cover the pistachio underneath evenly.
• Bake these bars until the edges look set but the middle still has a slight little jiggle to it—about 45 to 50 minutes.
• Take them out of the oven and let them cool completely on the counter until they reach room temperature (that's about 1 hour).

The Blackberry Topping

• While the bars are cooling, let's make that beautiful topping! Put your frozen blackberries and white sugar in a saucepan over a medium-low heat.
• Stir them often and let them cook until the berries have softened and released their lovely juices—about 10 minutes. Stir in the lemon zest.
• In a small bowl, whisk together 2 tablespoons of cornstarch and the lemon juice. Slowly pour this mixture into the warm blackberries, stirring all the while.
• Keep cooking and stirring until the berry mixture thickens up, which only takes another 1 to 3 minutes.
• Remove it from the heat and let it cool completely to room temperature, which will also take about 1 hour.

Finishing Touches

• Once your bars and your topping are both completely cooled, pour that gorgeous blackberry mixture over the bars and spread it into an even layer.
• Pop the pan into the refrigerator until the bars are completely chilled, which is at least 4 hours, or simply leave them there overnight.
• When you're ready to serve, sprinkle 2 tablespoons of chopped pistachios over the top.
• Use that parchment paper overhang to gently lift the bars right out of the pan, and then peel the paper away. Take a sharp knife, run it under hot water, and wipe it dry.
• Cut the bars into 16 squares, wiping the knife clean after every cut to keep them looking pristine. Store any extra bars safely in the refrigerator.