Line an 8.5 x 4.5-inch loaf pan with two long pieces of plastic wrap, leaving a few inches overhanging on all sides. This extra length will help cover the cake once assembled. Set the pan aside.

In a large mixing bowl, combine 3½ cups of heavy cream, peanut butter, powdered sugar, marshmallow creme, and vanilla extract. Using an electric mixer with a whisk attachment, start on low speed and mix until the ingredients begin to blend and thicken. Scrape down the sides of the bowl, gradually increase the speed to medium, and continue beating until the mixture reaches medium-to-stiff peaks, about one to two minutes.

Spoon about two-thirds of the peanut butter whipped cream into the prepared pan, spreading it evenly. With the long side of the pan facing you, stand the chocolate wafer cookies upright in neat rows, fitting about 12 to 14 cookies per row. Continue arranging the cookies until the pan is filled with four rows. Spread the remaining peanut butter whipped cream over the cookies, smoothing the top with a spoon or offset spatula. If there is extra whipped cream, it can be saved for another use. Fold the overhanging plastic wrap over the top and refrigerate for at least six hours or freeze for about four hours for a firmer texture.

To prepare the chocolate ganache, combine the chocolate chips, ⅔ cup of heavy cream, and corn syrup in a microwave-safe bowl. Heat in 30-second intervals, stirring in between, until the mixture is smooth and glossy, about 90 seconds in total. Let cool to room temperature, about 30 minutes. Reserve 1 tablespoon of the ganache for later use.

Carefully invert the chilled cake onto a serving plate and remove the plastic wrap. Pour the ganache over the top, allowing it to cascade down the sides. Use a spoon or offset spatula to spread it evenly. Return the cake to the refrigerator to let the ganache firm up while preparing the final topping.

In a clean mixing bowl, whip the remaining ½ cup of heavy cream on medium speed until soft-to-medium peaks form, about one minute. Gently swirl 1 to 2 teaspoons of the reserved ganache into the whipped cream, creating streaks rather than fully mixing. Spoon the topping onto the cake and, if desired, garnish with extra chocolate wafer cookies. Slice and serve immediately.