Line a 9"x9" baking pan with parchment paper, allowing for overhang, and lightly oil the paper.

Lightly toast 1 cup of pistachios in a dry skillet over medium heat for 3–4 minutes, shaking the pan, then chop finely and reserve 1/4 cup for topping.

In a medium bowl, combine graham cracker crumbs, 3/4 cup finely chopped pistachios, melted butter, and 2 tbsp sugar. Mix until the crumbs hold when squeezed.

Press the mixture firmly into the bottom of the prepared pan in an even layer, using a measuring cup to compact the crust.

Chill in the fridge for 15 minutes while preparing the chocolate layer.

Place 6 oz of dark chocolate in a heatproof bowl.

Heat 3/4 cup heavy cream in a small saucepan until it just begins to simmer. Pour the hot cream over the chocolate and let it sit for 1 minute, then stir until smooth and glossy.

Pour the ganache over the chilled crust and smooth to the edges. Chill for 20–30 minutes until set but still tacky.

In a bowl, beat together softened cream cheese and powdered sugar until smooth, then add vanilla.

Melt the white chocolate gently, and fold it into the cream cheese mixture. Optionally, blitz 1/4 cup of pistachios into a coarse paste and fold into the cream cheese mixture.

Spread the pistachio-cream mixture carefully over the slightly set ganache, smooth it out, and chill for at least 1 hour.

Melt the remaining 2 oz of dark chocolate and drizzle decoratively over the top.

Sprinkle with reserved chopped pistachios and a light pinch of flaky sea salt.

Use the parchment overhang to lift the slab from the pan, and slice into 12 squares with a sharp knife. Keep chilled until serving.