Make the coffee mixture. Pour the cooled coffee into a shallow dish. Stir in the liqueur or rum, if using. Keep it at room temperature so the ladyfingers absorb evenly.

Whip the cream. In a cold mixing bowl, whip the heavy cream with the vanilla and a pinch of salt until soft peaks form. Don’t overwhip—soft peaks will give you a silky, spreadable texture.

Mix the mascarpone filling. In a separate bowl, beat the mascarpone with the sugar just until smooth and combined. Fold the whipped cream into the mascarpone mixture in two additions, using a spatula to keep it airy.

Set up your dish. Use an 8x8-inch or 9x9-inch square dish (or a similar 2-quart dish). A glass dish makes the layers visible, but any will work.

Dip the ladyfingers. Quickly dunk each ladyfinger into the coffee mixture for about 1–2 seconds per side. They should be moist but not falling apart. Arrange them in a single layer to cover the bottom of the dish.

Spread the first cream layer. Spoon half of the mascarpone mixture over the ladyfingers. Smooth it gently to the edges with an offset spatula or the back of a spoon.

Repeat the layers. Add another layer of dipped ladyfingers. Top with the remaining mascarpone mixture and smooth the surface.

Dust with cocoa. Sift a light, even layer of unsweetened cocoa powder over the top. This adds a pleasant bitterness and classic look.

Chill to set. Cover the dish and refrigerate for at least 4 hours, preferably overnight. The flavors meld and the texture firms up beautifully.

Garnish and serve. Before serving, dust with a little more cocoa and add chocolate shavings if you like. Slice into squares with a sharp knife, wiping the blade between cuts for clean layers.