Heat the oven to 325°F and fit parchment into an 8-inch square baking pan, leaving enough paper extending above the sides to use as handles. The paper should sit against the bottom so the crust can form an even layer.

Stir the graham cracker crumbs, sugar, melted butter, and optional cinnamon together in a small bowl, then gently press the mixture across the pan bottom. The crumbs should hold together without becoming a tightly compressed slab.

Bake the crust for 8 to 9 minutes, then transfer the pan to a wire rack to cool. Look for light browning rather than a deeply toasted surface.

Beat the softened cream cheese in another bowl for 3 to 4 minutes. It should become smooth and spreadable, with no firm pieces remaining.

Mix in the pistachio butter, sugar, sour cream, lemon juice, lemon zest, and vanilla for 2 to 3 minutes. The mixture should look glossy and evenly blended, often with a muted pale green color that varies with the pistachio butter.

Add the lightly beaten eggs in three additions, incorporating the equivalent of one egg at a time on low speed and stopping as soon as each addition blends in. The batter should stay smooth rather than becoming airy or foamy.

Use a spatula to fold in 1/2 cup chopped pistachios, spread the filling over the cooled crust, and scatter the remaining pistachios over it. The nuts should sit throughout the filling and across the top without pockets of unmixed batter.

Bake for 35 to 40 minutes, checking the pan with a gentle nudge near the end. The edges should look set and slightly puffed, while the center moves with a small, cohesive wobble rather than a loose ripple.

Let the cheesecake cool to room temperature, then refrigerate it for 2 hours or until cold. The filling should feel firm enough to hold its shape when lifted and sliced.

Lift the cold cheesecake onto a cutting board using the parchment handles and cut it into 9 bars. Each piece should have a defined edge and a crust that supports the filling.