a 9-by-3-inch (23-by-7.5-centimeter) springform pan
For the milk chocolate ganache: Place the chocolate and salt in a medium heatproof bowl and set aside. In a small saucepan, heat the cream over medium-high heat just until bubbles begin to form around the edges.
Pour the warm cream over the chocolate and salt and let sit for 1 minute so it begins to melt. Gently whisk together until fully incorporated and shiny.
Let come to room temperature, stirring occasionally, until it thickens and is less like chocolate syrup and pours more like hot fudge.
(To make ahead, let cool to room temperature, cover, and refrigerate for up to 1 week. Reheat over medium-low heat until liquefied.)
For the pudding: In a large saucepan, combine the granulated sugar, cornstarch, and salt. Add the milk and cream and whisk to combine. Add the eggs, whisk again, and place the saucepan over medium-high heat, whisking constantly.
Once the mixture begins to thicken and bubbles begin popping on the surface, turn the heat to medium and whisk vigorously for 45 seconds. Remove the pan from the heat.
If the pudding has any lumps, strain it through a medium-mesh wire sieve into a heatproof bowl. Add the peanut butter, butter, and vanilla and whisk until they are incorporated.
The pudding should be used almost immediately; it should still be warm and relatively pourable when you layer it with the crackers.
For the whipped cream: Refrigerate the bowl of a stand mixer and the whisk attachment (or a medium metal bowl and beaters from a hand mixer) until quite cold, about 15 minutes.
Once chilled, remove the bowl and whisk from the refrigerator, add the cream, and whip it on medium speed until just thickened.
Add the peanut butter, confectioners' sugar, and vanilla and, on medium-high speed, whip the cream until it holds stiff peaks that stand upright when the whisk is raised. Use it immediately.
To assemble: Lightly coat the sides of your springform pan with cooking spray, and line the sides of the pan with a 3-by-29-inch (7.5-by-75-centimeter) strip of parchment paper. Using a small offset spatula or the back of a spoon, spread a generous layer of the pudding on the bottom of the pan.
Cover as much of the pudding as possible with a layer of the graham crackers, filling any gaps with broken crackers. The pieces should touch. The goal is a solid layer of crackers.
Generously spread a layer of the ganache over the crackers.
Continue layering in this order (pudding, graham crackers, ganache) until you run out or reach the top of the pan. Spread the whipped cream on top of the cake. Gently cover the cake with plastic wrap, place it on a platter (to protect the inside of your refrigerator from any escaping ganache while the cake sets up), and refrigerate for 24 hours. (If you want to frost the sides of the cake with whipped cream, prepare the whipped cream after the cake sets up for 24 hours, and frost the top and sides just prior to serving.)
Peel the plastic wrap from the cake and run a paring knife between the paper and the pan. Open the clamp, remove the pan sides, and gently peel back the parchment paper. Transfer the cake, still on the pan bottom, to a serving platter. Decorate with chopped chocolate-covered peanut butter cups or roasted, salted peanuts. Using a knife, slice into wedges and serve.
Adapted from "Icebox Cakes" by Jessie Sheehan with permission by Chronicle Books, 2015.