In the bowl of an electric mixer using a whisk attachment, whisk the heavy cream and powdered sugar until stiff.
Crush one-third of the wafers by hand or with a rolling pin inside a resalable plastic bag until they become coarse crumbs. Set aside.
In a round 9-inch springform pan, layer in one-third of the whipped cream, smoothing evenly with a spatula. Then layer half of the remaining flat whole wafers close to each other, then one-third more of the whipped cream, then the remaining whole wafers and finally top with the rest of the whipped cream. Garnish the top of cake with the crushed wafers.
Cover and refrigerate for at least 6 hours.
Run a paring knife around the springform pan and release the wall of the pan from around the cake. Leave the cake on the bottom of the pan and transfer to a serving dish or cake stand, then slice and serve.