1. Prepare the Custard: In a pot, whisk the egg yolks with sugar until smooth and pale. Add the flour gradually, then slowly pour in the milk and vanilla extract, stirring to avoid lumps.
2. Cook the Custard: Place the pot on medium heat, stirring constantly until the mixture thickens into a creamy custard. Divide the custard in half and add a spoonful of cocoa powder to one half to create chocolate custard. Let both custards cool.
3. Assemble the Layers: Quickly dip the ladyfingers in Alchermes liqueur, then layer them in a serving dish. Spread a layer of vanilla custard over the ladyfingers, followed by a layer of chocolate custard.
4. Repeat and Chill: Continue layering until all ingredients are used up. Finish with a dusting of cocoa powder on top, and refrigerate for at least 2 hours.

Enjoy!