Lightly grease a 9x13-inch baking dish with nonstick spray or a thin layer of butter. Optionally, line with parchment paper, leaving an overhang on the long sides for easy lifting and slicing.
In a medium bowl, combine the graham cracker crumbs, granulated sugar, and 1/4 teaspoon fine sea salt. Pour in the melted butter and stir until the mixture is evenly moistened and resembles wet sand.
2 1/2 cups graham cracker crumbs, 1/2 cup unsalted butter, 1/4 cup granulated sugar, 1/4 teaspoon fine sea salt
Transfer the crumb mixture to the prepared pan. Use the bottom of a measuring cup or flat glass to press it firmly and evenly over the bottom of the pan. For no-bake method, chill the crust in the refrigerator for 20–30 minutes while you prepare the next layer. For a firmer crust, you may bake at 350°F (175°C) for 8–10 minutes, then cool completely before continuing.
In a large mixing bowl, beat the softened cream cheese with an electric mixer on medium speed until smooth and fluffy. Add the powdered sugar and vanilla extract and beat again until creamy and well combined.
8 ounces cream cheese, 1 cup powdered sugar, 1 teaspoon pure vanilla extract
If using heavy whipping cream, pour it into the cream cheese mixture and beat on medium-high until thick, light, and holding soft peaks. If using whipped topping, gently fold it into the cream cheese mixture with a spatula until fully blended and smooth. The mixture should be thick but spreadable.
1 cup heavy whipping cream
Once the crust is firm and cooled if baked, dollop the cream cheese mixture evenly over the crust. Carefully spread it into an even layer, taking care not to disturb the crumbs. Smooth the top, then place the pan in the refrigerator to chill while you prepare the pumpkin layer.
In a clean mixing bowl, whisk together the instant vanilla pudding mixes and cold milk for about 2 minutes, until the mixture begins to thicken. Add the pumpkin puree, pumpkin pie spice, ground cinnamon, and 1/4 teaspoon fine sea salt. Whisk until smooth and fully blended. Let stand a few minutes to thicken to a spoonable pudding consistency.
15 ounces pumpkin puree, 2 boxes instant vanilla pudding mix, 2 cups milk, 1 teaspoon pumpkin pie spice, 1/2 teaspoon ground cinnamon, 1/4 teaspoon fine sea salt
Remove the pan from the refrigerator. Spoon the pumpkin pudding mixture in dollops over the chilled cream cheese layer, then gently spread it into an even layer, trying not to disturb the layer beneath. Smooth the top.
Top the pumpkin layer with the whipped topping or homemade whipped cream, spreading it evenly all the way to the edges. Swirl the top with the back of a spoon for a decorative finish, if desired.
2 cups whipped topping, OR homemade whipped cream for topping
Cover the pan gently with plastic wrap or foil. Refrigerate for at least 4 hours, or preferably 8 hours or overnight, until the layers are fully set and the bars slice cleanly.
Just before serving, garnish the top as desired with crushed graham crackers or gingersnaps, a light sprinkle of cinnamon or pumpkin pie spice, a drizzle of caramel sauce, and/or chopped toasted pecans or walnuts. Leave a portion plain if serving nut-free guests.
crushed graham crackers or gingersnaps, ground cinnamon or pumpkin pie spice, caramel sauce, chopped toasted pecans or walnuts
Using a sharp knife, cut into 15–20 bars, wiping the blade with a warm, damp cloth between cuts for neat edges. Serve chilled.