Brew the espresso or strong coffee and pour it into a wide, shallow bowl to cool completely; stir in the Marsala wine or rum if using.

In a large heatproof bowl, whisk the egg yolks and sugar together until the mixture is pale yellow and slightly thickened.

Place the bowl over a pot of simmering water (double boiler method) and whisk constantly for about 10 minutes until the sugar dissolves and the mixture is warm to the touch, then remove from heat and let cool slightly.

Whisk the room temperature mascarpone cheese into the egg yolk mixture until smooth and well combined.

In a separate chilled bowl, whip the heavy cream using an electric mixer until stiff peaks form.

Gently fold the whipped cream into the mascarpone mixture using a spatula, being careful not to deflate the air, until the cream is uniform.

Quickly dip each ladyfinger into the cooled coffee for just 1-2 seconds per side (do not soak them or they will fall apart) and arrange a single layer in the bottom of an 8x8 inch baking dish.

Spread half of the mascarpone cream mixture evenly over the layer of ladyfingers.

Repeat the process with a second layer of dipped ladyfingers and top with the remaining mascarpone cream, smoothing the surface.

Cover the dish with plastic wrap and refrigerate for at least 4 hours, or preferably overnight, to allow the flavors to meld and the cream to set.

Just before serving, generously dust the top with unsweetened cocoa powder using a fine mesh sieve.