Place 8 ounces cream cheese on the counter and let sit at room temperature until softened, about 45 minutes. Meanwhile, line an 8x8-inch baking pan (about 2 inches high) with 2 sheets of parchment paper, positioning them perpendicular to each other, so that the parchment hangs about 2 inches over all 4 sides of the pan to form a sling.

Place 2 (about 3.9-ounce) packages instant chocolate pudding and 3 cups cold whole milk in a large bowl. Whisk until dissolved and the mixture is slightly thickened, about 2 minutes. Let sit to thicken while you prepare the crust and other layers.

Melt 1 stick unsalted butter in a small microwave-safe bowl in 20-second bursts until mostly melted, 40 to 60 seconds total (it will melt completely as it sits). (Alternatively, melt the butter in a small saucepan over medium heat.) Set aside to cool slightly.

Break 12 whole graham cracker sheets into rough pieces and place in a food processor fitted with a blade attachment. Add 2 tablespoons granulated sugar and ⅛ teaspoon of the kosher salt. Process until the crackers are the texture of sand, about 15 seconds. Add the butter and pulse to combine, 6 to 8 (1-second) pulses. (If using graham cracker crumbs, just stir 1 ½ cups crumbs and the butter together in a medium bowl.)

Transfer the mixture to the baking pan. Use the bottom of a measuring cup or your fingers to press the crumbs into an even layer, making sure to reach the edges and fill the corners. Refrigerate while you prepare the filling.

Place 1 ½ cups cold heavy cream and ¼ cup of the powdered sugar in the bowl of a stand mixer (or large bowl if using an electric hand mixer). Beat with the whisk attachment on high speed until stiff peaks form, 2 to 4 minutes. Transfer to another bowl.

Place the cream cheese, remaining ¼ cup powdered sugar, 1 teaspoon vanilla extract, and remaining ¼ teaspoon kosher salt in the bowl of the stand mixer (no need to wipe clean). Beat with the whisk attachment on medium speed until light and very fluffy, scraping down the sides of the bowl with a flexible spatula halfway through, about 3 minutes total.

Transfer 1 cup of the whipped cream to the cream cheese mixture and gently fold together with a flexible spatula until just combined. Dollop the cream cheese mixture into the baking dish and spread into an even layer.

Dollop the chocolate pudding over the cream cheese mixture and spread in an even layer. Dollop the remaining whipped cream over the chocolate layer and spread into an even layer. Cover and refrigerate for at least 4 hours or up to overnight.

When ready to serve, use a vegetable peeler to shave 1 (2-ounce) piece chocolate over the top if desired. Grasping the excess parchment, transfer the chocolate delight slab to a cutting board. Cut into 12 pieces, wiping the knife between each cut for cleaner cuts.