Line an 8x8-inch square baking pan with parchment paper, leaving an overhang on two opposite sides to form a sling. Lightly coat the pan and parchment paper with cooking spray.

Process 6 ounces vanilla wafer cookies and 2 tablespoons granulated in a food processor until fine crumbs form, about 20 seconds. Drizzle in 6 tablespoons melted unsalted butter and pulse until evenly moistened, about 5 (1-second) pulses. (Alternatively, place the cookies in a re-seleable plastic bag and crush with a rolling pin into fine crumbs. Transfer to a medium bowl and stir in the sugar and butter.)

Transfer to the baking pan and press it firmly into an even layer with the bottom of a flat measuring cup or your hands. Freeze for 15 minutes.

Whisk 2 (3.4-ounce) boxes vanilla instant pudding mix and 2 ½ cups of the cold heavy cream together in a large bowl until smooth; it will be very thick. Spread evenly over the crust. Refrigerate for at least 10 minutes. After about 5 minutes, make the ganache.

Place 6 ounces chopped semi-sweet chocolate in a medium heat-proof bowl. Bring ⅔ cup heavy cream to a full simmer in a small saucepan over medium heat. Pour over the chocolate and let it sit for 1 minute. Whisk until the chocolate is melted and the ganache is smooth.

Let cool for 3 minutes if you’d like to pour on the ganache for a smooth finish, or let cool for 5 minutes if you’d like to make a swooping pattern in the ganache.

Pour the ganache over the custard in an even layer. Use the back of a spoon or butter knife to make a swooping pattern in the ganache if desired. Refrigerate until set, at least 2 hours. Grasping the excess parchment, lift the slab out of the pan and place on a cutting board. Cut into 12 or 16 pieces, wiping the knife clean between each cut for the cleanest-looking slices.