01 - Whisk egg yolks and sugar in a heatproof bowl over gently simmering water (bain-marie) until the mixture is pale and slightly thickened, about 3–4 minutes. Remove from heat and allow to cool slightly.
02 - Fold mascarpone cheese and vanilla extract into the yolk mixture, blending until completely smooth and creamy.
03 - In a separate bowl, whip heavy cream to stiff peaks. Gently fold the whipped cream into the mascarpone mixture until evenly combined.
04 - Combine cooled espresso and coffee liqueur (if using) in a shallow dish.
05 - Quickly dip each ladyfinger into the coffee mixture for 1–2 seconds per side. Arrange a single layer in a 9 x 9 inch dish.
06 - Spread half of the mascarpone cream mixture evenly over the ladyfingers.
07 - Add a second layer of dipped ladyfingers, followed by the remaining mascarpone cream. Smooth the top evenly.
08 - Cover and refrigerate for at least 4 hours or preferably overnight to set properly.
09 - Dust the surface generously with unsweetened cocoa powder and sprinkle with dark chocolate shavings if desired before serving.