Make the soak: Stir the cooled espresso with the coffee liqueur and sugar (if using) in a shallow bowl or pie plate. Set aside.
Whip the pumpkin base: In a large bowl, whisk the pumpkin puree, mascarpone, powdered sugar, vanilla, cinnamon, ginger, nutmeg, cloves, and salt until completely smooth. Cold mascarpone lumps — make sure it is at room temperature.
Whip the cream: In a separate chilled bowl, beat the very cold heavy cream to stiff peaks with a hand mixer or stand mixer (about 2–3 minutes). Do not overbeat into butter.
Fold: Add about one-third of the whipped cream to the pumpkin-mascarpone mixture and stir to lighten it. Then gently fold in the remaining whipped cream in two additions, using a spatula, until no streaks remain. The mixture should be thick, fluffy, and hold soft peaks.
First layer: Quickly dip each ladyfinger into the espresso — one second per side, no more — and arrange in a single tight layer in a 9x7-inch (or 8x8-inch) dish. Trim or snap cookies to fill gaps.
Layer the cream: Spread half of the pumpkin mascarpone cream evenly over the ladyfingers.
Second layer: Repeat with another dipped layer of ladyfingers, then spread the remaining pumpkin cream over the top, smoothing it with an offset spatula.
Chill: Cover and refrigerate at least 4 hours, but overnight is best — the ladyfingers fully soften and the slices hold clean edges.
Serve: Just before serving, dust the top generously with cocoa powder mixed with the extra cinnamon. Slice with a hot, dry knife, wiping between cuts, and serve chilled.