In a large mixing bowl, whisk egg yolks and sugar together until thick and pale.
In another bowl, whip the heavy cream to stiff peaks.
Fold the mascarpone cheese into the yolk mixture until smooth.
Gently fold in the whipped cream until combined.
In a shallow bowl, combine coffee and liqueur if using.
Quickly dip each ladyfinger into the coffee mixture and line the bottom of a 9x13 inch dish.
Spread half of the mascarpone mixture over the ladyfingers.
Repeat with a second layer of dipped ladyfingers and remaining mascarpone cream.
Cover and refrigerate for at least 4 hours or overnight.
Dust with cocoa powder and garnish with chocolate shavings before serving.