Start by preparing the custard.
Blend egg yolks and sugar in a bowl until they're pale and thick.
In a saucepan over medium heat, slowly mix the egg yolk mixture with whole milk.
Cook until the mixture thickens, then set aside to cool.
Once the custard is cool, fold in the mascarpone cheese gently.
Stir until you have a smooth blend.
Mix instant coffee and hot water to create your coffee mixture.
Dip ladyfingers briefly in this mix and lay them out in your serving dish.
Pour half of the custard mixture over the ladyfingers, smoothing it out.
Repeat the layering process, finishing with a final layer of custard on top.