Lightly grease a 9×13-inch glass or ceramic baking dish with a thin layer of butter or nonstick spray so the crust releases easily when sliced.
In a medium bowl, combine the graham cracker crumbs, granulated sugar, and a pinch of fine sea salt. Pour in the melted butter and mix until all crumbs are evenly moistened and the mixture feels like damp sand when squeezed.
2 cups graham cracker crumbs, 1/2 cup unsalted butter, 1/4 cup granulated sugar, fine sea salt
Transfer the crumb mixture to the prepared dish. Press it firmly into an even layer with the bottom of a measuring cup or flat glass, paying extra attention to the corners. Refrigerate for at least 20 minutes while you prepare the next layer.
In a large bowl, beat the softened cream cheese with an electric mixer on medium speed until smooth and fluffy, about 2 minutes, scraping down the sides of the bowl to eliminate lumps.
8 oz cream cheese
Add the powdered sugar and vanilla to the cream cheese and beat until smooth. Gently fold in 1 cup of thawed whipped topping. If the mixture is too thick to spread easily, add 2–3 tablespoons of milk, a little at a time, until silky and spreadable but not runny.
1 cup powdered sugar, 1 teaspoon pure vanilla extract, 1 cup frozen whipped topping, 2-3 tablespoons milk
Remove the chilled crust from the fridge. Carefully spread the cream cheese mixture over the crust, starting from the center and working outward to avoid pulling up crumbs. Smooth the top and chill again for 15–20 minutes.
In a clean bowl, whisk the instant pistachio pudding mixes with 3 cups of very cold milk for about 2 minutes, until thickened but still pourable and creamy.
2 boxes instant pistachio pudding mix, 3 cups cold milk
Gently pour or spoon the prepared pistachio pudding over the chilled cream cheese layer. Spread it into an even layer, keeping it level for a neat presentation.
In a small bowl, stir the remaining 2 cups of whipped topping with up to 2 tablespoons of milk if needed to loosen slightly. Carefully spread this over the pistachio pudding, floating it lightly so the layers stay distinct.
2 cups frozen whipped topping, 2 tablespoons milk
Sprinkle chopped pistachios, extra graham crumbs, white chocolate, and/or fresh fruit over the top as desired. Cover the dish tightly with plastic wrap and refrigerate for at least 4 hours, or overnight, until the layers are fully set.
1/2 cup chopped roasted pistachios, crushed graham crackers or shortbread cookies, fresh raspberries, strawberries, or pomegranate arils, shaved white chocolate or white chocolate chips
For clean bars, use a sharp knife and wipe it between cuts. Use a small offset spatula to lift out the first piece, then serve chilled.