In a medium bowl, whip the heavy cream with 1/4 cup granulated sugar and vanilla extract until stiff peaks form. Set aside.
In a separate bowl, beat the softened mascarpone cheese until smooth.
In another bowl, whisk the egg yolks with the remaining 1/4 cup granulated sugar until pale and thick.
Gently fold the egg yolk mixture into the mascarpone cheese until well combined.
Fold the whipped cream into the mascarpone mixture until smooth and creamy.
If using, lightly brush each ladyfinger with raspberry liqueur. If not, you can skip this step.
Arrange a single layer of ladyfingers in the bottom of an 8x8 inch baking dish. Break them if necessary to fit.
Spread half of the mascarpone cream mixture over the ladyfingers.
Scatter half of the fresh raspberries over the cream layer.
Repeat the layers: another layer of ladyfingers, the remaining mascarpone cream mixture, and the remaining raspberries.
Cover the dish with plastic wrap and refrigerate for at least 4 hours, or preferably overnight, to allow the flavors to meld and the ladyfingers to soften.
Before serving, dust with cocoa powder or garnish with additional raspberries, if desired.
Notes
For an alcohol-free version, you can soak the ladyfingers in a mixture of raspberry juice and a little sugar.