In a large bowl, whisk the yolks of the Large Egg (6) with Granulated Sugar (1/4 cup) until pale and doubled in volume and the mixture maintains a "ribbon" when folded over itself, 3 to 5 minutes. Add the Mascarpone Cheese (16 ounce) in 2 or 3 additions, whisking well to combine. Add the Kahlua (2 fluid ounce) if using, and whisk to combine.
In a clean bowl or the bowl of a stand mixer fitted with a whisk attachment, whip the 4 Egg Whites and remaining Granulated Sugar (1/4 cup) to soft peaks. Fold the egg whites into the mascarpone mixture in two or three additions.
In a roughly 6x9-inch casserole or plate with a border, spread about one third of the mascarpone cream into an even layer. Soak each individual Ladyfingers (16) in the Espresso (1 1/2 cup) and arrange them very tightly on top until the cream is completely covered.
Spoon the remaining cream over the cookies, spreading it into an even layer. If desired, you can pipe additional cream onto the top to make it look nicer.
Refrigerate for at least 1 hour or up to 2 days to set the cream. Just before serving, dust the top with Unsweetened Cocoa Powder (to taste). Serve and enjoy!