1. Prepare the crust layer by mixing graham cracker crumbs with melted butter until it resembles wet sand, then press it into the bottom of your serving dish to form an even layer. Optionally, bake the crust in an oven preheated to 350°F for 8-10 minutes or leave it no-bake.
2. In a mixing bowl, beat cream cheese until smooth, then gradually add powdered sugar and vanilla extract, mixing until fully incorporated. Fold in a portion of the whipped topping to keep the mixture fluffy, and spread this over the crust evenly.
3. Whisk pistachio pudding mix with whole milk in a separate bowl, stirring until it thickens. Spread the pudding mixture evenly over the cream cheese layer, ensuring there are no clumps.
4. Layer the remaining whipped topping over the pistachio pudding, smoothing it out evenly for a polished top layer.
5. Sprinkle chopped pistachios or other optional toppings (like mini marshmallows, mandarin oranges, or maraschino cherries) over the whipped topping for an extra decorative and flavorful touch.
6. Refrigerate the Pistachio Ambrosia Lush for at least two hours to allow it to chill, set, and for the flavors to meld perfectly.
7. Serve chilled by slicing into uniform squares or slices and enjoy this creamy, nostalgic dessert.