Make the espresso coffee, and mix with 2 Tbsp sugar while hot, then add some water (to end up with 8 oz/237 ml). The end result should be to your liking; not too strong, or too weak, is best.

Set up a double boiler (if you don't have one) by placing a glass bowl over a bit of hot water (the bowl should not touch the water) over low heat. Beat the egg yolks and remaining sugar off the heat for a few minutes, then transfer the bowl over to the barely simmering water in the pot until the temperature reaches 150 degrees F, or 65 C. Continue beating for 2 minutes, then allow to cool, stirring occasionally so it doesn't create a skin.

Add the mascarpone to the egg and sugar mixture, and stir until well-combined.

Pour some cold coffee into a bowl. Be sure it's not hot or the biscuits will absorb too much liquid.

Start dipping the Savoiardi biscuits into the coffee, once on each side. Do this quickly  (no more than one second each side), then place each one on the platter (or in the dish) in a row (this is the original method). Continue until you have enough for one layer (my platter fit 9 cookies in length). Do not use more than 10 cookies. Next, spread half of the mascarpone/egg mixture over the soaked biscuits.

Repeat with the other half of the biscuits for the second layer.

Finally, spread with the rest of the filling, cover with cling film and refrigerate for at least 4 hours, but preferably overnight. When ready to serve, remove from the refrigerator, and dust generously with cocoa (from a sieve).

To serve, slice into even pieces, wiping the knife in between each cut to produce clean edges, and serve using a metal spatula (for best results).