In a heatproof bowl set over a pot of gently simmering water, whisk together the egg yolks and 1/2 cup of sugar constantly for 8-10 minutes until thickened.

Remove from heat and let cool to room temperature.

In a separate bowl, beat the mascarpone cheese until smooth. Gently fold the cooled egg yolk mixture into the mascarpone until well combined.

In another bowl, whip the heavy cream with the remaining 1/4 cup of sugar until stiff peaks form.

Gently fold the whipped cream into the mascarpone mixture in two additions.

In a shallow dish, combine the cooled espresso with the coffee liqueur, if using.

Quickly dip each ladyfinger into the coffee mixture for one second on each side and arrange them in a single layer in a 9x9-inch dish.

Spread half of the mascarpone mixture evenly over the ladyfingers.

Repeat the layering process with the remaining ladyfingers and top with the remaining mascarpone mixture.

Cover and place in the refrigerator for at least 6 hours, or ideally overnight.

Before serving, dust the top generously with cocoa powder and add dark chocolate shavings if desired. Cut into squares and serve chilled.