In a large bowl, whip 1 1/2 cups heavy cream with the powdered sugar until soft peaks form. In a small bowl, stir the peanut butter until soft and creamy and whisk in the remaining 1/2 cup heavy cream. Whisk together until the mixture is light and fluffy. Fold the peanut butter mixture gently into the large bowl of whipped cream until well combined.
On a cake platter, serving tray or large plate, dab the bottom of 7 cookies with a tiny amount of cream mixture and arrange 6 of the cookies in a circle with the remaining cookie in the middle of the circle. Spread about 2/3 cup cream mixture on top of the cookies, spreading the cream outward to cover all but the outer edges of the cookies (an offset spatula really helps this process!). Repeat the layers 5 more times, each time staggering the cookie layer and topping the cake with the remaining cream.
Refrigerate the cake for at least 8 hours (or up to 2 days).
Slice into pieces and serve chilled.
Notes
Plan Ahead: this cake requires at least 8 hours of chilling time so plan ahead! Wafers: the Nabisco Famous Wafers are the most widely available chocolate wafers; however, if you are so inclined, I've seen several homemade recipes online.