Beat the softened cream cheese in a large bowl with a hand mixer on medium speed until completely smooth, about 2 minutes. Scrape down the sides. Add the pumpkin puree, brown sugar, pumpkin pie spice, cinnamon, vanilla, and salt. Beat again until light and fluffy with no streaks, about 2 more minutes.

In a separate cold bowl, whip the heavy cream with the powdered sugar on high speed until it holds firm, stiff peaks. This takes about 3 to 4 minutes with a hand mixer. The cream should not flop over when you lift the beaters.

Gently fold about one-third of the whipped cream into the pumpkin cream cheese mixture using a rubber spatula. Use slow, sweeping strokes from the bottom of the bowl upward. Once mostly combined, fold in the remaining whipped cream in two more additions. Stop folding when the mixture is uniform and light in color. Do not stir or you will deflate the cream.

Spread a thin layer of the pumpkin cream cheese filling across the bottom of a 9x13 inch dish, just enough to anchor the first cookie layer. Lay cinnamon wafer cookies in a single layer over the filling, covering the bottom as evenly as you can. Break cookies to fill gaps at the edges.

Spread a generous, even layer of the pumpkin cream cheese filling over the cookies using an offset spatula or the back of a large spoon. Aim for about 1/3 of the filling per filling layer. Add another layer of cookies on top, then another layer of filling. Repeat once more so you have 3 cookie layers and 3 filling layers, finishing with a filling layer on top.

Dust the top evenly with pumpkin pie spice using a small fine-mesh strainer or your fingertips for a light, even coating.

Cover the dish tightly with plastic wrap and refrigerate for at least 8 hours, or overnight. The cookies absorb moisture from the filling and soften into a tender, cake-like texture. Do not rush this step.

When ready to serve, use a sharp knife to cut clean slices. Wipe the blade between cuts for the neatest presentation. Serve cold, straight from the dish.