Spread a very thin layer of plain whipped topping over the bottom of the loaf pan. This helps the first cookie layer stay put and creates a neat base.
Lay a single layer of chocolate wafer cookies over the whipped topping, breaking a few cookies as needed so they fit snugly in the pan. Try to cover as much surface as you can without big gaps.
Spread a generous layer of plain whipped topping (about 1/2 cup) over the cookies, smoothing it gently with the back of a spoon or an offset spatula. You don’t need perfection, just even coverage.
Add another layer of chocolate wafer cookies on top of the whipped topping, again fitting them snugly. Repeat the process of alternating layers of cookies and whipped topping until you reach about 1/2 inch below the top of the pan. Finish with a cookie layer if you can, pressing lightly so the stack settles.
Spread the chocolate-cocoa whipped topping mixture over the final cookie layer, smoothing it into an even, chocolatey blanket. This will create a darker band just under the final white top.
Finish with a thick, fluffy layer of the remaining plain whipped topping, mounding it slightly in the center and smoothing the surface. The top should look like a soft, snowy cap over the dark cookie layers.
Using a small fine-mesh strainer or sifter, dust a light veil of cocoa powder over the top. Aim for a gentle, even sprinkle rather than heavy patches—it should look softly speckled, not buried.
Cover the loaf pan tightly with plastic wrap or foil. Refrigerate for at least 6 hours, but preferably overnight. During this time, the chocolate wafer cookies will soften and turn cake-like, and the layers will firm up for clean slicing.
When ready to serve, remove the plastic wrap. If you used parchment, run a thin knife around the edges and use the parchment overhang to gently lift the cake from the pan onto a cutting board. For an easy, casual presentation, you can also slice it directly in the ceramic loaf pan, just as it sat in the fridge.
Use a sharp knife dipped in hot water and wiped dry between cuts to slice the cake into thick pieces. You should see distinct dark cookie layers softened into the whipped topping, with a fluffy white top dusted in cocoa. Serve slices cold on small plates and watch how quickly the platter empties at your potluck.
