Fill a large pot about three-quarters full with water and bring it to a gentle simmer. Place a glass bowl on top to check the level, the bottom should just lightly touch the water. Once you’ve checked, remove the bowl and set it aside.
Separate the eggs, keeping only the yolks and saving the whites for another recipe. Add the yolks to the bowl (off the pot) and begin whisking by hand for about 5 minutes, until they start to lighten in colour.
Add the sugar gradually, in three stages, whisking well after each addition so it dissolves properly.
Place the bowl over the pot of water, making sure it sits securely without trapping the steam. Keep whisking continuously while the mixture cooks gently from the heat below.
Make sure the water stays at a gentle simmer, never boiling. Slowly pour in the alcohol, in this case Frangelico, while continuing to whisk.